Several people have died and more than 50 are in hospital after a huge fire raged through the night at a west London tower block, a fire chief says.
Eyewitnesses said they saw people trapped inside the burning Grenfell Tower, in north Kensington, screaming for help, and shouting for their children to be saved.
Firefighters, still at the scene, rescued “large numbers” of residents.
The 24-storey block, now smoking ruins, looks at risk of collapsing.
Eyewitnesses said they saw lights – thought to be mobile phones or torches – flashing at the top of the block of flats, and trapped residents coming to their windows – some holding children.
The Met Police has set up an emergency number on 0800 0961 233 for anyone concerned about friends or family.
London Fire Commissioner Dany Cotton said there had been “a number of fatalities” but she could not say how many because of the “size and complexity” of the building.
She urged all residents to make sure they had reported themselves to police so that the authorities know they are safe.
The cause of this “unprecedented incident” was not yet known, she said, and it was too early to speculate on the building, although it was structurally safe enough for her crews to be working inside.
Paul Munakr, who lives on the seventh floor, managed to escape.
“As I was going down the stairs, there were firefighters, truly amazing firefighters that were actually going upstairs, to the fire, trying to get as many people out the building as possible,” he told the BBC.
He said he was alerted to the fire not by fire alarms but by people on the street below, shouting “don’t jump, don’t jump”.
Eyewitness Jody Martin said: “I watched one person falling out, I watched another woman holding her baby out the window… hearing screams.
“I was yelling at everyone to get down and they were saying ‘We can’t leave our apartments, the smoke is too bad on the corridors.'”
Michael Paramaseevan, who lives on the seventh floor with his girlfriend and young daughter, said he ignored official advice to stay in your home.
“If we had stayed in that flat, we would’ve perished. My gut instinct told me just to get the girls out. I wrapped the little one up because of the smoke and I just got them out.”
Another resident, Zoe, who lives on the fourth floor, said she was woken by a neighbour banging on her door.
“The whole landing was thick with smoke. The smoke alarms weren’t going off but the way it spread so quickly from the fourth floor, all the way up to the 23rd floor was scary.”
The BBC’s Andy Moore, who was at the scene, described watching debris falling from the building, and hearing explosions and breaking glass.
“The police keep pushing back their cordons, pushing back members of the public for fear the building might collapse,” he said.
London Mayor Sadiq Khan said questions will need to be answered over the safety of tower blocks.
“We can’t have 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,” he told BBC Radio.
Matt Wrack, of the Fire Brigades Union said something had clearly gone badly wrong with fire prevention procedures at the building.
Firefighters would normally fight a fire in a tower block from the inside, going up the fire escape, and fighting using the internal dry-rising mains, he said, but that’s not been possible in this case.
“Several hundred” people would have been in the block when the fire broke out, leader of Kensington and Chelsea Borough Nick Paget-Brown said.
Appeals are being made on social media for news of missing friends and relatives, who might have been caught in the blaze.
An emergency rest centre has been opened for those now homeless at the Harrow Centre, in Freston Road. There are also local collections under way for spare clothes, toys and toiletries.
The first reports of fire in the tower, in Latimer Road, on the Lancaster West Estate, came in at 00:54 BST. Three hours later, people were still being evacuated from the tower, the police said.