Sixty firefighters are tackling a blaze at the famous Camden Lock Market in north London.
The London Fire Brigade (LFB) said on Monday morning that eight fire engines had been dispatched to reports of a fire at the popular tourist spot.
Footage posted on social media showed firefighters dousing a significant fire.
The LFB tweeted: "Eight fire engines and around 60 firefighters have been called to reports of a fire in #Camden Lock Market."
One witness tweeted: "On a night bus I just passed the start of a big fire in Camden, now at Euston I've seen lots of ambulances head north."
Another said: "Just drove past Camden market and there's a huge fire on top a building, close to the Loch Bridge! Crazy crazy scenes."
A major blaze ravaged the area in 2008, shutting the attraction for several months.
A Metropolitan Police spokeswoman said: "Police were called on Monday at 12.10am to Camden Lock Market to reports of a fire. London Fire Brigade were already at the scene when officers arrived. It is unknown at this stage if any persons are injured, we await update."
LFB urged people to avoid the area, adding that it had raised the number of fire engines at the scene to 10, with 70 firefighters tackling the blaze.