Lancaster West Estate tower in the early hours of Wednesday when most of the residents would have still been in bed.The fire broke out in the 27-story
The fire brigade said 45 fire engines and 200 firefighters as well as 20 ambulances were sent to the building which has 120 flats and was built in 1974, but recently underwent a major refurbishment.
"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.
Several people are trapped inside the building with reports that it might collapse.
Mayor of London Sadiq Khan said a "major incident" had been declared.
A witness told CNN that he saw people jumping from the building.
Police officials said that they had started an evacuation of the block and the neighboring buildings, adding some people were being treated at the scene for smoke inhalation.
At least 30 people were taken to hospital on Wednesday. "We can confirm that we have taken 30 patients to five hospitals," London Ambulance Service said.
The streets around the tower have been sealed off and there is a chaos there with "people in night clothes, no shoes, crying, looking for family.”
George Clarke, the presenter of Channel 4 TV program Amazing Spaces, told Radio 5 Live, "I'm 100 meters 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."
"People can be seen at the windows, including one man waving a blanket from the window," a witness told The Guardian.
"Some shouting "put your head out the window” or calling the man with the blanket to shout his flat numbers so they can guide the fire services to him."