Trafalgar Square was covered in smoke following a fire at the Admiralty Pub in Spring Gardens, a street that crosses the east end of the Mall by Trafalgar Square.
The London Fire Brigade sent 20 fire engines and 125 firefighters to the scene.
Crews were dealing with the blaze long into the night in the pub basement, working in arduous, challenging and hot conditions.
The LFB announced the blaze was under control just after 10pm this evening.
Three hours after the Brigade arrived on the scene, a spokesperson said "steady progress" was being made in tackling the blaze, but added "we’re likely to be at the scene for hours to come".
In a statement on Twitter, the London Fire Brigade said: "It’s a hot night so crews are taking on a lot of water. Please spare a thought for all firefighters dealing with fires in these conditions.”
The pub said on Twitter: “Due to the current situation The Admiralty is closed until further notice. We’ll update our website and social channels in due course.”
Around 150 people were evacuated. There are no reports of any injuries at this stage.
Firefighters rushed to the scene in central London
London Fire Brigade
Smoke billowed from the Trafalgar Square pub
GB News
Firefighters responding to the blaze in London
GB News
The blaze sparked an immediate response in Trafalgar Square
GB News
Station Commander Keith McDermott, who was at the scene, said: “The fire is in the basement of a pub in Trafalgar Square.
"As a result there will be heavy traffic disruption and we ask people to avoid the area if possible.”
He added: "Due to the arduous, challenging and hot conditions inside the basement we've increased the number of fire engines and firefighters at the scene.
"Around 150 people evacuated the pub and surrounding businesses before the Brigade arrived. There has been no reports of any injuries."
In an earlier statement on Twitter, the London Fire Brigade said: "Half of the basement is alight.
"Please avoid the area if possible as there will be heavy traffic disruption."
The cause of the fire is currently being investigated, but the news follows an ongoing heatwave – with today's temperatures soaring as high as 30C.
The Mall between Trafalgar Square and Horse Guards Road was closed in both directions following the incident.