The London Fire Brigade said 40 fire engines and 200 firefighters were on the scene in White City in north Kensington. The alarm was raised around 1.15am on Wednesday.

The London Ambulance Service said it has taken 30 patients to five hospitals while police say a "number of people are being treated for a range of injuries", including smoke inhalation, as pictures from the scene showed flames shooting metres into the sky and engulfing most of the block.

The Guardian newspaper reports more than 200 people live in the burning Grenfell Tower, which is part of a large housing estate. It said some were being treated for smoke inhalation.

CNN reported that a witness said people were jumping from the burning building.

A witness told BBC radio "It's just an inferno. I can hear people screaming, 'help me, help me', but the building to too big."

As dawn broke, columns of thick black smoke continue to rise from the building and ashes filled the air, as firefighters tackled the blaze form the ground.

Actor and writer Tim Downie, who lives around 600 metres away said he feared the block could collapse.

"I have seen people coming out in their bedclothes - it's just very distressing."

Residents are being evacuated from the tower block, the Metropolitan Police said.

The London Fire Brigade said the cause of the fire was not known at this stage. At 6.30am local time it said 30 adjacent flats have been evacuated by police. 

George Clarke, who presents Channel 4 show Amazing Spaces, told Radio 5 Live: "I'm 100 metres away and I'm absolutely covered in ash.

"It's so heartbreaking, I've seen someone flashing their torches at the top level and they obviously can't get out.

"The guys are doing an incredible job to try and get people out of that building, but it's truly awful."

Met Police said cordons were in place and advised that the estate and surrounding area were to be avoided.

"At this stage we are aware of two people being treated at the scene for smoke inhalation. We await an update as to whether there are any further injuries," the Met said in a statement.

The estate is on Latimer Road, White City.

The fire brigade said the fire extends from the second to the 24th floor of the building.

There has been a long-running dispute between some residents of the tower block and the management agency.

A community organisation called the Grenfell Action Group had expressed worry about fire in the building following an earlier incident in 2013.

The group said it was their "conviction...that a serious fire in a tower block or similar high density residential property" would expose the management company's practices. 

The Grenfell Action Group said the tower had "narrowly averted a major fire disaster...in 2013 when residents experienced a period of terrifying power surges that were subsequently found to have been caused by faulty wiring."