Workers cutting away the old metal roof in the John Street Market in Bradford accidentally set fire to a stall with a spark from a blow torch.
Fire crews from Bradford and Fairweather Green helped contractors tackle the fire which happened at 2.15am today.
The market is in the final stages of a £4 million refurbishment which includes the replacement of its old roof with a higher cover.
Station Officer David Swales said: "The contractors were using hot metal cutting equipment, an oxy-propane torch I think, on the roof and a spark got inside one of the centre stalls.
"They reaction pretty quickly and broke into the stall and used the market's internal hose reels to stop the spread of the fire. The stall was quite badly damaged and the building was smoke logged."
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