A man suffered 40 per cent burns when a stockpile of firecrackers in his house in Bowbazar caught fire, setting off multiple low-intensity explosions in the congested neighbourhood on Tuesday.

Eight houses, including the one where the firecrackers had been stocked, were completely gutted before 12 fire engines could douse the flames.

Babu Karmakar, the owner of the house in Baburam Seal Lane near Goenka College of Commerce, is a supplier of crackers. His family was not in the house at the time of the incident.

His neighbour Gopal Parui was watching television around 10.30am when he heard a series of low-intensity explosions.

"I rushed out and saw Babu's house on fire," he said. "The explosions were continuing. Some of the local youths pulled him out of the house."

Babu is being treated at the Calcutta Medical College and Hospital. His wife Aruna said her husband used to source crackers from various manufacturing units in Howrah and South 24-Parganas and sell them at shops in Calcutta.

After supplying to retailers, Babu would keep residual stock of firecrackers such as bottle rockets and fire shells in his house.

Bastab Baidya, the deputy commissioner of police, central division, visited the spot but refused to say anything.

An officer of Muchipara police station said a complaint had been lodged against Babu. "We don't know the exact quantity of crackers Babu had stocked. Since he is in hospital we haven't been able to question him," he said. "Preliminary investigation has revealed that he had stocked the crackers illegally because he had no permission."

A fire officer said traces of "explosives" that could have triggered the fire had been found. "The exact nature of explosives will be determined only after a forensic test."