Fire engulfed a 24-storey block of flats in central London on Wednesday, killing some people, injuring at least 50 more and trapping some residents asleep inside the towering inferno.
200 firefighters, backed up by 40 fire engines, fought the blaze for hours in the north Kensington area.
Thick black and grey smoke billowed high into the air over London hours after the blaze broke out at the Grenfell Tower where several hundred people live.
Residents rushed to escape through smoke-filled corridors in the housing block after being woken up by the smell of burning. Some said no fire alarm sounded.
Witnesses said they saw trapped residents desperately shouting for help from windows on upper floors as flames enveloped the building.
London Fire Brigade said the fire engulfed all floors from the second to the top of the block which contained 130 apartments.
"In my 29 years of being a fire fighter, I have never ever seen anything of this scale," London Fire Brigade Commissioner Dany Cotton told reporters.
"I am very sad to confirm that there have been a number of fatalities, I cannot confirm the number at this time due to the size and complexity of this building."
London Ambulance Service said more than 50 people had been taken to hospital.
"I looked through the spy hole and I could see smoke everywhere and the neighbours are all there. There's a fireman shouting 'get down the stairs'," one of the block's residents, Michael Paramasivan, told BBC radio. "It was an inferno."
"As we went past the fourth floor it was completely thick black smoke. As we've gone outside I'm looking up at the block and it was just going up. It was like pyrotechnics. It was just unbelievable how quick it was burning."
The cause of the fire, which broke out just before 1 am (0000 GMT), was not known, the Fire Brigade said.