- The fire is under control, but the the building is still smoldering.
- At least 50 people have been taken to five London hospitals.
- There are fears that the building, with more than 100 apartments, might collapse.
- A hazardous area response team were also dispatched.
London Mayor Sadiq Khan declared a "major incident" after the blaze engulfed the Grenfell Tower in North Kensington just before 1 a.m local time Wednesday. Around 200 firefighters, 40 fire trucks and 20 ambulance crews were at the scene.
A website run by the "Grenfell Action Group" said residents of the tower had expressed concerns over the safety of the building, specifically pointing to fire risks. Fire chiefs said it was too early to speculate on the cause of the blaze.
It is unclear how many people are still in the building, but witnesses who escaped reported terrifying accounts of people trapped in the tower as they fled. Some people were reported to have jumped from the building while witness described seeing people, including children, banging on windows, screaming and crying for help.
London Fire Brigade Commissioner Dany Cotton there had been "a number of fatalities" but she could not confirm how many. "In my 29 years of being a firefighter, I have never seen anything of this scale," she said.
There were fears that the building, which houses more than 100 apartments, might collapse. It was not yet possible to confirm the cause of the fire, which spread throughout the building from lower floors, Cotton said.
'Spreading like wildfire'
One resident of the tower, Michael Paramasivan, said he was watching TV as his girlfriend and daughter slept when he smelled burning plastic. Soon he saw the smoke and chaos.
"I grabbed my little girl and ran down the stairs," he said. "Half of the building was ablaze by the time we got out. And it was just spreading like wildfire."
"(If I were asleep), we would have all been dead -- that's how bad it was," he said.
Tia Abrahams, who lives close to the scene, got there before the fire brigade.
"There were people banging on windows screaming, crying out for help. There was even young children banging on the windows. It wasn't good," she told CNN. "These were about 4 or 3-year-old children who I can imagine didn't understand what was going on."
"As the fire progressed, you could hear screams of agony from people," she said. "It was horrible."
She did not know if the children managed to get out.
Ayyube Asif told CNN he saw the fire from his cousin's house miles away and immediately ran toward the blaze. He and his cousin have family living on the 18th floor of Grenfell and wanted to make sure they were OK.
"We brought them out and we held them in our arms, and the paramedics brought them to the hospital," Asif said. "You can't get away from a fire on the 18th floor, but God's grace, they got away."
Kayo Mnemimeh saw lights flickering at the top of the building and thought it was a signal from residents.
"Literally within five minutes of seeing that, that side of the building became engulfed in flames. I can't say whether they got out or not," he said.
He saw another man on about the 11th floor. "He came to the window, and there was fire all around where his flat was," said Mnemimeh.
Firefighters started spraying water cannons around him. He was still trapped there when Mnemimeh spoke to CNN, and he's not sure what happened to him.
Grenfell Tower was built in the 1970s and recently subject to a $10.9 million redevelopment, according to property firm Rydon. The building was to undergo specific improvements to fire safety and ventilation works.
The web page relating to the refurbishment works later appeared to have been wiped.
The tower, part of the Lancaster West social housing estate, is managed by an agency on behalf of the London Borough of Kensington and Chelsea.
Former fire marshal Robert Rowe told CNN the fire appears to have been "moving very quickly."
He said he suspects the fire sprinkler system "was out of service or there was a malfunction at the time" based on how quickly the fire spread.
"What a fire sprinkler does, is stop it immediately. You won't have a fire of (such) a magnitude," Rowe said. "It would stop it right there."
Close to Notting Hill, the tower block is around a five-minute walk from the Latimer Road Underground station and near the Westfield shopping center in the west London suburbs. It's a mixed-development property that houses a boxing gym and a nursery, according to a news release last year from the Royal Borough of Kensington and Chelsea. Before the renovation there were 120 apartments in the building.
Investigation in its early stages
The blaze appears to be the worst since a 2009 fire in south London killed six people, including three children.
"This is an absolutely devastating fire," Nick Paget-Brown, the local council leader, told CNN. "By all accounts, it spread quickly."
He told CNN it was not yet clear how many people were evacuated or how many people are receiving support.
"We need more information. This is an early stage of an awful incident," he said. "We have a clear emergency plan for dealing with the immediate incident and then there will need to be a thorough plan for helping residents who have lost their homes."
In a statement, London's Metropolitan Police Service said people are being treated for a range of injuries.
The London Fire Brigade said the cause of the fire is still unknown. In a statement posted on Facebook, the service said the "fire is from the second floor to the top floor."
"Firefighters wearing breathing apparatus are working extremely hard in very difficult conditions to tackle this fire. This is a large and very serious incident and we have deployed numerous resources and specialist appliances," Assistant Commissioner Dan Daly said.