- Huge blaze at London's Grenfell Tower, 40 fire engines at spot
- Police said they were evacuating the block
- Number of people being treated for a range of injuries: officials
Witnesses could hear screaming from the upper floors as the flames rose and one desperate resident could be seen waving a white cloth. London Ambulance Service said they have taken 30 patients to five hospitals in the city.
Police and fire services attempted to evacuate the concrete block and said "a number of people are being treated for a range of injuries", including at least two for smoke inhalation.
The fire brigade said 40 fire engines and 200 firefighters had been called to the blaze in Grenfell Tower, which has 120 flats.
The ambulance service said it had sent more than 20 ambulance crews to the scene.
"Fire is from 2nd to top floor of 27 storey building," the fire service said on Twitter.
Firefighters at the scene said they had managed to evacuate residents up to the 11th floor.
Police were also clearing out nearby buildings because of fears about falling debris.
"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," he said.
London mayor Sadiq Khan tweeted: "Major incident declared at Grenfell Tower"
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".
The apartment block was built in 1974.
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 Grenfell 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.