Reports from the scene say the fire is spreading quickly and has consumed part of the Hawley Arms, a popular Camden Pub
which is frequented by celebrities including singer Amy Winehouse.
Revellers from local pubs and bars have been moved away from the danger area, where flames are leaping up to 30ft in the air.
Crowds have been dispersed because of fears there may be gas canisters within the area.
Twenty fire appliances and about 100 firefighters are in attendance.
London Ambulance Service said it has ambulances and a hazardous response team at the scene.
Onlooker Eric Braun, who lives in the area, said: "The back of the Hawley Arms...is well on fire."
He added: "The flames are not shooting up nearly as high as before but a lot of the market is burned. But there are still ferocious flames.
"The fire has jumped over the Silverlink railway and the railway bridge has been pretty well scorched."
Camden Town is a major tourist attraction attracting up to 300,000 visitors each weekend to its six open-air and indoor markets and vibrant mix of bars, clubs, shops and restaurants.