Huge fire engulfs 27-storey Grenfell Tower apartment block in London

The 27-storey apartment block in West London engulfed in flames. (Photo: Screengrab from Reuters video)

Witnesses could hear screaming from the upper floors as the flames rose and one desperate resident could be seen waving a white cloth.

Police said they were evacuating the block and "a number of people" were being treated for a "range of injuries" including two for smoke inhalation.

Forty fire engines and 200 firefighters had been called to the Grenfell Tower apartment block which has 120 residential units and was built in 1974.

A statement from the brigade said the fire started from the second storey of the building and spread to the top.

Police said in a statement they were called at 1:16am (0016 GMT) "to reports of a large fire at a block of flats in the Lancaster West Estate".

"Firefighters wearing breathing apparatus are working extremely hard in very difficult conditions to tackle this fire," London Fire Brigade assistant commissioner Dan Daly said. "This is a large and very serious incident and we have deployed numerous resources and specialist appliances."

Images and videos from the scene have been circulating on social media showing the huge flames.

Mayor of London Sadiq Khan tweeted that a "major incident" has been declared at Grenfell Tower in Kensington.

A person was seen at a window of the residential tower block in the early hours, as firefighters tackled the blaze.

Witnesses said they heard screams for help from inside the building, The Guardian reported.

Actor and writer Tim Downie, who lives nearby, said: "It's horrendous. The whole building is engulfed in flames. It's gone. It's just a matter of time before this building collapses".

The BBC reported debris falling from the building and that explosions were heard along with the sounds of glass breaking.

Local residents had warned a year ago about a potential fire risk caused by rubbish being allowed to accumulate during improvement works.

"This matter is of particular concern as there is only one entry and exit to Grenfell Tower during the improvement works," read a blog post by the Greenfell Action Group.

"The potential for a fire to break out in the communal area on the walkway does not bear thinking about as residents would be trapped in the building with no way out," it said.