Firefighters are battling at "huge" blaze at a construction site in central London.
London Fire Brigade confirmed 10 fire engines and 50 firefighters were called to the fire at 12.45pm on Great Portland Street, near Oxford Street and the headquarters of the BBC.
A number of gas cylinders are involved in the blaze, it said on Twitter, and an exclusion zone of 25 metres has been set up "as a precaution".
"Some cylinders can explode when exposed to heat," LFB wrote in a tweet.
Witnesses shared footage of thick smoke and flames leaping up a scaffold structure surrounding a building on the road.
Serious fire on Langham Street / Great Portland Street, W1 pic.twitter.com/8n3a93WRg9— Paul Thompson (@raganello) February 17, 2018
Fire brigade arrived on Great Portland Street. Quite something. pic.twitter.com/ycTiieGQTS— Mukul Devichand (@MukulDevichand) February 17, 2018
Firefighters sprayer water at the building, which neighbours said is being converted into flats by developers.
Nearby, residents stood behind a police cordon waiting to be allowed back into their homes.
Huge fire in central London. Looks like Great Portland Street area. pic.twitter.com/7USqNy7l8v— Jonathan Savage (@JSavageTweets) February 17, 2018
More than 40 people called 999 about the fire, LFB said.
Calls to the fire service had suggested that the fire had either broken out close to or in a building site, an LFB spokesman said.
He added that firefighters had not confirmed what type of building was ablaze.
No injuries have yet been reported from the scene of the fire in London's West End, Scotland Yard said.
A spokesman said: "Police were called shortly before 12.50pm today to reports of a fire at a building site on Great Portland Street.
"The emergency services are on the scene and there are no reported injuries at this time."
Road closures are also in place, the spokesman added.