Kway chap stall owner Madam Oh was in the midst of preparing eight packets of food for a customer at the Old Airport Road Food Centre yesterday morning when she heard a loud sound.

Startled, she looked up to see fire breaking out at Xin Mei Congee, a corner stall in the row opposite her outlet.

Recounting what she saw, Madam Oh, 53, said two workers, who looked to be in their 30s, were working on the gas pipes in the ground-floor stall, which was closed.

Suddenly, they shouted and leapt off the premises, but the face and arm of one of them were burned red, said Madam Oh, who declined to give her full name.

"I heard a "pop" sound, and then a big fire was burning," she said in Mandarin.

Madam Oh said the fire appeared to be contained within the stall but the flames were getting close to the ceiling. The area was not crowded then. Some people went to get water and fire extinguishers, while others made phone calls, she said.

Madam Oh turned off her gas pipe, covered her food, pulled the stall shutter down and left.

The Singapore Civil Defence Force (SCDF) said in a Facebook post that two men and a woman, with burns on their arms and hands, were taken to the Singapore General Hospital. A fourth casualty, who had a cut on his right hand, refused to be taken to hospital.

The SCDF cordoned off a small area affected by the fire. The other stalls were able to carry on with their business as usual, it said.

Preliminary investigations showed that the flash fire might have been caused by repairs being carried out to the stall's gas supply, the SCDF said. It sent a fire engine and two fire bikes, but the food centre's sprinkler system put out the fire before they arrived.

Madam Oh said she still felt safe using the gas, as the pipe undergoes maintenance by the gas company about once a year.

She estimated that the affected stall would have to remain closed for at least a month for repairs.

"Earning a living will be a problem (for the stall owner)," she said.