Quick to react: With Muamba floored, referee Howard Webb immediately called on medical staff
Players and fans watched in horror as medics fought to save the stricken Bolton star's life.
The televised FA Cup clash with Spurs was abandoned as the player was rushed to hospital.
Muamba, 23, was taken to the Heart Attack Centre at the London Chest Hospital, where last night he was critically ill in intensive care.
Spurs striker Jermain Defoe, who was close to tears, declared on Twitter: "Pray for Fab, God willing he will pull through."
Tottenham team-mate Rafael van der Vaart, also visibly shaken, tweeted: "Terrible what happened. We're all praying for him."
Muamba suddenly collapsed near the halfway line after 41 minutes with the game at 1-1.
Six paramedics raced across the pitch and tried to resuscitate the England Under-21 star using a defibrillator.
ESPN cameras showed players and fans weeping as Muamba needed SIX minutes of treatment.
A heart doctor, who was in the crowd, also ran on to the pitch to help.
Muamba was carried off on a stretcher wearing an oxygen mask and flanked by medical staff who were still trying to resuscitate him as he was rushed to a waiting ambulance.
PFA chief executive Gordon Taylor added: "We are all waiting, hoping and praying. For all the football family it's a terrible thing to see."
Referee Howard Webb abandoned the game just before 6.30pm.
John Barnes, who was a Liverpool player when the Hillsbrough disaster claimed 96 lives, was commentating for ESPN.
He said: "When I saw what happened everything came flooding back to me.
"When there is something as serious as this, this is when football comes together. Football is a family and our thoughts are with him."
Fellow TV pundit Kevin Keegan added: "Everything pales into insignificance when you see something like that."
Both the FA and Premier League issued statements wishing Muamba well.
Stay strong! Get Well Soon!!!
God Bless You
jia you!!
i hope he's all right
Shrine: Well wishers have flocked to the Reebok Stadium to leave get well messages for Muamba
Liverpool fans in the Kop display their get well messages before the club's FA Cup tie against Stoke
Get well soon: Bolton fans have shown their support outside the club's Reebok Stadium home
Well-wishers: Bolton fans have been leaving shirts and scarves outside the stadium to show their support
I hope Fab Muamba pulls through. This incident has an eerie resemblance to what happened to Marc Vivien Foe at the Confederatioons Cup in Paris back in 2003.
Fabrice Muamba is treated under the gaze of Dr Deaner (far right)
Fabrice Muamba spent a second night fighting for his life with the football world praying for his recovery.
And the Daily Express can reveal an incredible turn of fate may have increased Muamba’s chances of survival after Tottenham fan Dr Andrew Deaner, a consultant cardiologist at the London Chest Hospital, raced on to the pitch to give his assistance.
Bolton midfielder Muamba suffered a cardiac arrest and collapsed in the 41st minute of their FA Cup quarter-final at Tottenham. His heart stopped beating on the White Hart Lane surface.
After more than seven minutes of treatment, Muamba was rushed to the London Chest Hospital in Bethnal Green, where he was sedated and put on to a life support machine.
It has emerged Dr Deaner, who ran on from Tottenham’s East Stand, stressed Muamba, 23, must go straight to the specialist hospital where he works.
Dr Deaner advised on the treatment immediately given, then accompanied Muamba in the ambulance and is now part of a team of experts giving round-the-clock care.
An expert told the Daily Express: “It is better to drive past two hospitals to get to the London Chest Hospital. Fabrice could not be in a better place.”
A statement from the Chest Hospital and Bolton, read: “Fabrice Muamba remains in a critical condition in intensive care.
"Fabrice received prolonged resuscitation at the ground and on route to The London Chest Hospital, where his heart eventually started working. Fabrice remains anaesthetised in intensive care and will be for at least 24 hours.”
Muamba was screened by Bolton at the start of the season and the club perform annual ECGs on their players.
Bolton manager Owen Coyle said: “Fabrice’s family have asked me to pass on their thanks for the many, many kind messages of support from not only Bolton fans but also fans from clubs across the country and abroad.”
The Premier League granted Bolton’s request to postpone their match at Aston Villa tomorrow. And it is believed some Bolton players have questioned whether the tie against Tottenham should be replayed at all.
Fabrice Muamba of Bolton Wanderers who is in a critical condition
The hospital treating Bolton star Fabrice Muamba has confirmed the player can now recognise family members and respond to their questions.
Forty-eight hours after he collapsed during an FA Cup quarter-final tie against Tottenham at White Hart Lane, where he suffered a cardiac arrest, it is the clearest indication yet that Muamba is winning his battle for life.
"Fabrice Muamba remains in intensive care at the London Chest Hospital and is continuing to show signs of improvement this evening," said the joint statement released by the London Chest Hospital and Bolton.
"He is now able to breathe independently, without the aid of a ventilator and he is able to recognise family members and respond to questions appropriately. These are positive signs of progress.
"However, his condition remains serious and our medical staff in intensive care will continue to monitor and treat him.
"His family and club would like to thank the media for continuing to respect their privacy at this time."
The confirmation follows claims from Curtis Codrington, who says he is a friend of Muamba and is one of only 83 people followed by the player on social networking site Twitter, that he had started speaking in French and English.
Bolton sources have told Press Association Sport that the 23-year-old has made considerable progress and the signs are looking extremely positive for the player.
However, they are cautioning against over-optimism, pointing out that it is not unknown for patients to plateau at this stage and that Muamba remains wired up and is still officially on the critical list.
Nevertheless, the latest updates are more than Bolton's anxious players, staff and supporters dared hope as medics battled for two hours to get Muamba's heart beating again after it stopped at White Hart Lane.
The player's fiancee, Shauna Muamba, wrote on Twitter: "All your prayers are working people thank u so so much. Every prayer makes him stronger. To God be the glory."
Earlier, speaking for the first time since the game, Bolton captain Kevin Davies said Muamba owed his life to the support he received almost instantly.
"There is no doubt in my mind if it wasn't down to all those people, we wouldn't even be in this situation," said Davies.
Bolton have not confirmed how long manager Owen Coyle intends to maintain his own vigil for the player, although he is expected to remain in the capital for a further two days.
That would throw into question Bolton's ability to fulfil Saturday's scheduled Premier League game with Blackburn at the Reebok Stadium.
The Lancashire derby may go a long way to determining whether Bolton will remain in the Premier League this season.
It is understood there is enough flexibility within the fixture schedule for that game to be postponed, although the rescheduled FA Cup tie with Tottenham would take precedence in any rearrangement and that would normally take place at some point next week.
However, that game is far from Coyle's mind at the moment.
"We are all after the same objective; to see that lovely young man, who has such a fantastic smile. That's what we want to see again," said the Scot this lunchtime.
"When you look through what he's come through in his life already, he's a natural fighter.
"Also, he's a physically fit young man so I think those two things will be a source of help and encouragement."
Muamba left his home in war-torn Congo in 1999 and was reunited with his father, who had fled five years earlier and sought asylum in Britain after becoming a target for rebels.
The 23-year-old has overcome such a difficult start in life to become an England Under-21 international, joining Arsenal as a youth team player, before moving onto Birmingham and then Bolton for £5million in 2008.
Though not one of the most flamboyant players, Muamba was amongst the most industrious, which just makes the shock at what has happened even more acute for Bolton skipper Kevin Davies, who spoke today for the first time since the weekend drama unfolded.
"We all love Fabrice," said Davies.
"I respect him hugely for coming from where he was to where he is now.
"He is one of the first into training and has worked extremely hard to better himself. He is always out there doing a bit extra.
"That is the reason why he has been so successful and has a massive career ahead of him."
Bolton's players had a team meeting at their Euxton training complex this morning to be given the latest bulletin.
They already knew the scheduled encounter with Aston Villa tomorrow had been postponed.
However, Davies said Bolton's next game was the last thing on his mind.
"Any of those questions are irrelevant at the minute," he said.
"Decisions will have to be made but my immediate thoughts are with Fabrice and his family.
"The club will take a stance on it in the next couple of days. But at the minute we want to just try and help Fabrice."
Life savers: The four doctors who treated Fabrice Muamba - heart specialist Dr Andrew Deaner, consultant cardiologist Dr Sam Mohiddin, Tottenham doctor Shabaaz Mughal and Bolton doctor Jonathan Tobin
Heroes: The four doctors chat outside the London Chest Hospital
Fabrice Muamba was given 15 defibrillator shocks and his heart stopped for 78 minutes - but he has now told Bolton's doctor: 'I'm fine.'
Jonathan Tobin has revealed details of the extraordinary efforts to save the midfielder's life after he collapsed on the pitch against Tottenham on Saturday.
Muamba remains in intensive care at the London Chest Hospital but there is now growing optimism that he will make a full recovery.
He was visited by Thierry Henry, who briefly played with him during their Arsenal days together, on Wednesday afternoon.
Bolton have also confirmed that they will return to White Hart Lane next Tuesday to replay the cancelled FA Cup quarter-final match.
Tobin said: 'I'm glad to say that the early signs of recovery have continued. I went to see Fabrice last night. I went in and he said "Hi, doc".
'I asked him how he was and he said "Fine". I explained to him what had happened. That's the sort of level of communication I have had with Fabrice.'
Tobin - who gave mouth-to-mouth resuscitation to Muamba - also admitted he was left 'fearing the worst' after the player required 15 separate shocks - two on the pitch, one in the tunnel and another 12 in the ambulance on the way to the hospital.
Support: Bolton fans posted more messages for Muamba at the Reebok Stadium
Favourite: Dozens of messages were scribbled on this poster of the stadium
None of these worked as his heart failed to restart for 78 minutes in the frantic efforts to revive him.
After working on Muamba for 48 minutes before his arrival at hospital, Dr Tobin confirmed the player continued to receive treatment for 30 minutes before his heart showed signs of activity.
'In effect he was dead in that time,' Tobin said. 'Fabrice was in a type of cardiac arrest where the heart is showing lots of electrical activity but no muscular activity.
'It's something that often responds to drugs and shocks. Now heaven knows why, but Fabrice had, in total, 15 shocks. He had a further 12 shocks in the ambulance.'
Having such an intimate knowledge of Muamba, once he arrived at the hospital on Saturday, Tobin went to a corridor and broke down as he feared the consequences of what had happened.
It was the first chance he had to think. What happened previously was just a blur.
'I can't begin to explain the pressure that was there,' Tobin said. 'This isn't somebody that's gone down in the street or been brought into A&E.
'This is somebody that I know, I know his family. This is somebody I consider a friend. This is somebody I joke with on a daily basis. As I was running onto the pitch I was thinking "Oh my God, it's Fabrice".'
The feelings were just as acute when Muamba grasped Tobin's hand for the first time.
Backing from the stars: Lionel Messi wears a tribute t-shirt on Tuesday night after Emmanuel Adebayor's visit
Indeed, the Congo-born player's entire recovery has been described as 'miraculous' by Dr Andrew Deaner, the cardiologist and Tottenham fan who leapt from his seat in the crowd and rushed onto the pitch to help.
'If you're going to use the term miraculous, I guess it could be used here,' he said.
Dr Deaner went to visit the player after he had woken up and recalled that Muamba was able to make a joke even that early in his recovery process.
'I whispered into his ear "What's your name?",' he said before the answer 'Fabrice' came back.
Dr Deaner went on: 'I said "I understand you're a very good footballer". And he said "I try".'
All this news, following first-hand reports of Muamba's condition from Kevin Davies, Nigel Reo-Coker, Darren Pratley and Mark Davies, meant that when Coyle spoke to his players at training to see whether they wanted to face Blackburn this weekend, the response was unanimous.
Bolton will then return to Tottenham on Tuesday to replay the FA Cup match with the blessing of Fabrice Muamba's fiancee and family.
Muamba is like a soldier. His first thought when he regained consciousness was the result of the (subsequently-abandoned) match.
Actually, I am VERY VERY VERY curious about what is going through his mind when he's dead during that 2 hours...
Does he sense he's in heaven or another place? Was he just feeling as if asleep? Does he know anything at all during that 2 hours when he's "dead"? Does he dream during those 2 hours? Does he know he's in danger? How's he feeling during the 2 hours? Perhaps calm and happy because he didn't realize he is in danger?
So many questions. =(