Twelve people have been killed and 78 have been treated at hospitals following a huge fire at a west London tower block.
Massive flames licked up the sides of Grenfell Tower on the Lancaster West Estate as 200 firefighters battled the blaze along with 40 fire engines. Plumes of black smoke were still billowing into the air hours after the blaze was sparked.
Police said they expected the number of fatalities to rise.
"Sadly I can confirm that there are now 12 people who have died, that we know of," Police Commander Stuart Cundy said.
"This is going to be a long and complex recovery operation."
Eyewitnesses said they saw people trapped inside the tower - in north Kensington - screaming for help, and shouting for their children to be saved.
London Ambulance said 78 people had been treated in hospital. It said 34 people remained in hospital and 18 were in critical care.
The Fire Service said it had rescued large numbers of people.
The spokesperson said it was too early to speculate on the integrity of the building before the blaze, but it was currently safe for fire personnel to be inside the structure fighting the fire.
Fire crews would be tackling the fire for at least the next 24 hours, the London Fire Brigade said.
"It has been a very large and very significant fire, I anticipate the London Fire Brigade will be on scene dealing with this fire for at least the next 24 hours," London Fire Commissioner Dany Cotton said.
The fire was first reported about 1.15am Wednesday local time, when many residents would have been asleep in their beds.
The building is social housing, managed by Kensington & Chelsea Tenant Management Organisation on behalf of the council.
The Ministry of Foreign Affairs and Trade said there was no indication that any New Zealanders had been caught up in the fire.
'I heard children calling out for help' - witness
A witness, Safyha, told BBC the fire had spread from one side of the building to engulf the entire tower.
"I heard children calling out for help... I think I saw people clinging to the outside of the building trying to climb down the building - I mean, it's just horrific."
Eyewitness Jody Martin told the BBC: "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.'"
Tower 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."
CNN reported people were jumping from some of the upper floors.
Nearby residents were evacuated as a precaution.
Neighbours shouting to a man still visible in a window at Grenfell Tower pic.twitter.com/oUh7HgD08i— Alice Ross (@aliceross_) June 14, 2017
At Portobello Rugby Club, Kayo Mneimneh, 31, and Hassan Filali, 26, described watching the tragedy unfold and how the fire suddenly flared up to engulf floors where people were trapped.
They told AAP that a tower resident told them an exploding fridge had started the fire.
"The moment the fire raised up to the top on one side, on the other side people were flickering their lights to show people they were there," Mr Mneimneh said.
It's believed mobile phone lights and torches were used as distress signals.
"Within five minutes of the flickering lights the fire had engulfed where the flickering lights were coming from," Mr Filali said.
Mr Mneimneh said a woman was standing beside him speaking on the phone to people trapped inside the block, who were telling her they couldn't come down because there was fire outside their door.
"Moments after that the fire just took over, I'm not sure what happened to them, if they managed to get out."
The pair said fire ladders were too short to reach the higher storeys but a crane was used to try to reach a man they could see at a window.
That plan had to be abandoned after bits of the building began falling on the crane but they believed the man was eventually rescued.
They also witnessed someone using what they thought was a duvet to climb down from the fourth or fifth floor and they had heard of someone jumping from the other side of the building.
Fire was a 'major incident' - London mayor
London Mayor Sadiq Khan said questions would need to be answered over the safety of tower blocks.
Reuters reports that some residents said they had been advised they should stay in their flats in the event of a fire, while the block's residents association had previously warned it was worried about the risk of a serious fire.
"These questions are really important questions that need to be answered," Mr Khan told BBC Radio.
"Across London we have many, many tower blocks and 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."
He said a "major incident" had been declared. Police closed the A40, a major road leading out of west London, while some parts London's underground train network were closed as a precaution.
The cause of the fire is not known, the Fire Brigade said. Residents said repairs, including the addition of some sort of cladding, had been made to the exterior of the block recently.
- RNZ / Reuters / BBC