KOKO London, a music venue in the city’s Camden Town district, caught fire on Monday night. Dozens of firefighters are on the scene.
Images from scene show the roof of the club almost completely engulfed in flames.
The venue has been closed for around a year and was due to open this year after a £40 million refurbishment.
A spokesman for London Fire Brigade said: “We were called at 8.56 to a fire at a Camden nightclub under refurbishment. Thirty per cent of the roof is alight.
“Firefighters are working hard to save the rest of the building. Please avoid the area if possible.”
Sixty firefighters and six fire engines were sent to battle the blaze.