Authorities initially received the call at around 1:15 a.m. to the fire that stretched from the second floor to the top. Metropolitan Police said "an evacuation process is under way," the BBC reported.
There were indications that people were trapped in the burning building, according to media accounts. Trapped residents were reported to have built ropes from sheets to escape from windows.
"I'm 100 meters away and I'm absolutely covered in ash," one eyewitness told Radio 5 Live. "It's so heartbreaking, I've seen someone flashing their torches at the top level and they obviously can't get out."
The residential block holds 120 flats, according to the Daily Mail.
Here's video footage of the scene »
This is a developing story. Check back for updates.
40 fire engines & 200 firefighters have been called to the Lancaster West Estate tower block fire #NorthKensington https://t.co/SmtWbgGpSg pic.twitter.com/H4qgGmh52Y
- London Fire Brigade (@LondonFire) June 14, 2017
I really hope everyone got out ok. #PrayersForGrenfell #london #kensington #fire #GrenfellTowerFire pic.twitter.com/FHZ6cgMN9s
- Kevin W. (@kwilli1046) June 14, 2017
Grenfell Tower on fire outside my flat. Never experienced such terror in my life. Hope everyone is safe. pic.twitter.com/x5gJin5Ltl
- Xeni R (@xensxr) June 14, 2017