More than 200 firefighters, backed up by 40 fire engines, fought for hours to try to control the blaze, London's deadliest for a generation. The Grenfell Tower apartment block was home to about 600 people.
A local residents' group said it had predicted such a catastrophe on their low-rent housing estate that overlooks affluent parts of the Kensington area of the capital, and London Mayor Sadiq Khan said there were questions to answer.
Prime Minister Theresa May promised there would be a proper investigation into the disaster, which delayed her talks on trying to secure a parliamentary deal to stay in power and launch talks on Britain's exit from the European Union.
Some residents screamed for help from behind upper-floor windows and others tried to throw children to safety as flames raced through the Grenfell block of about 120 apartments just before 1 a.m.
Firefighters said they had rescued 65 people - some in pyjamas - from the 43-year-old block.
"We could see a lot of children and parents screaming for 'Help! Help! Help!' and putting their hands on the window and asking to help them," Amina Sharif told Reuters.
"We could do nothing and we could see the stuff on the side was falling off, collapsing. We were just standing screaming and they were screaming."
Tying sheets together
Another witness, Saimar Lleshi, saw people tying together sheets to try to escape.
"I saw three people putting sheets together to climb down, but no one climbed down. I don’t know what happened to them. Even when the lights went off, people were waving with white shirts to be seen," Lleshi said.
The fire sent up plumes of smoke that could be seen from miles away. The ambulance service said 68 people were being treated in hospital, with 18 in critical condition.
More than 16 hours after the fire started, crews were still trying to douse flames as they sought to reach the top floors.
But London police commander Stuart Cundy told reporters he did not believe further survivors would be found in the building.
At a nearby community center used to house some of those rescued, tensions were rising as occupants waited for news.
"The fire, which was unprecedented in its scale and speed, will be subject to a full fire investigation," said Steve Apter from the London Fire Brigade. "Any lessons learnt from this will be borne out not just across London, across the UK - and lessons learnt globally."
The emergency services said it was too early to say what had caused the inferno, which left the block a charred, smoking shell. Some residents said no alarm had sounded. Others said they had warned repeatedly about fire safety in the block.
The building had recently undergone an 8.7 million pound ($11.08 million) exterior refurbishment, which included new external cladding and windows.
"We will cooperate with the relevant authorities and emergency services and fully support their enquiries into the causes of this fire at the appropriate time," Rydon, the firm behind the refurbishment work, said in a statement.
Children thrown to safety
Residents who escaped told how they woke up to the smell of burning and rushed to leave through smoke-filled corridors and stairwells.
There were reports that some leapt out of windows. Other witnesses spoke of children including a baby being thrown to safety from high windows.
Tamara, one witness, told the BBC: "There's people, like, throwing their kids out, 'Just save my children, just save my children!'".
Opposition Labour party leader Jeremy Corbyn said sprinkler systems should be installed in such blocks and he called on the government to make a statement in parliament.
Fire Minister Nick Hurd said local authorities and fire services across the country would assess tower blocks undergoing similar renovation work to provide reassurance.
"In due course when the scene is secure, when it is possible to identify the cause of this fire, there will be proper investigation and if there are any lessons to be learned, they will be and action will be taken," May said.
Khan, the London mayor, said there needed to be answers after some residents said they had been advised they should stay in their flats in the event of a fire.
"What we can't have is a situation where people's safety is put at risk because of bad advice being given or, if it is the case, as has been alleged, of tower blocks not being properly serviced or maintained," Khan said.
Resident Michael Paramasivan told BBC radio he had spoken to a woman who lived on the 21st floor: "She has got six kids. She left with all six of them. When she got downstairs, there was only four of them with her. She is now breaking her heart."