An eighth-floor apartment in a 13-storey residential building on Southern Avenue caught fire on Tuesday morning, leaving several elderly residents gasping for air.

Many residents had to be assisted out of the building after the power supply to the elevators was shut off as soon as the fire was reported. Most of the 104 apartments in the 49-year-old building are occupied by elderly Calcuttans whose children live elsewhere in India or abroad.

The fire broke out in the bedroom of an eighth-floor flat at Ananda, 116 Southern Avenue, when a window air-conditioner caught fire.

Pinaki Sarkar, 74, a retired engineer, and his wife Mili, 70, were preparing for lunch at the time. The couple, who own flats on both the first and eighth floors of the building, had temporarily shifted upstairs as their first-floor residence was undergoing renovation.

“I was in the living room and my help was in the kitchen when I heard a loud sound. I went to the bedroom and saw flames. The window AC had caught fire and fallen,” said Mili Sarkar, standing outside their flat, 8H.

A large portion of the bedroom was gutted. “The saddest part is that our son’s bed — the one he grew up using — has been completely gutted,” she said.

The couple’s son lives in the US and their daughter in Australia.

They managed to rush out before the flames spread further. The family lost a laptop and Pinaki Sarkar’s wallet containing cards, which he later tried to block with the help of a neighbour.

Next-door neighbour Anju Majumdar, 80, whose daughter lives in Canada, was alerted by support staff. “Someone rang the doorbell and told me to step out immediately. By then, smoke had entered my flat,” she said.

A staff member carried her down eight floors to safety.

Four fire tenders were pressed into service to douse the flames.

“The fire started inside an apartment on the eighth floor. The exact cause has yet to be ascertained,” said an officer of the fire and emergency services department.

Residents and building staff acted as first responders before firefighters arrived.

“We used fire extinguishers and hose pipes to spray water, but there was so much smoke in the hallway that we couldn’t reach the source of the fire,” said Rabi Ranjan Gupta, secretary of the residents’ association.

For many, the incident underscored the larger concern of evacuation challenges in a building where most residents are elderly.

“A majority of the flat owners are elderly people. Their children live outside Calcutta or abroad,” said a resident. “My greatest fear is how they will come down from the upper floors if the elevators are shut during a fire.”

Local MLA Debasish Kumar visited the building.

The incident comes a day after the outdoor unit of an AC caught fire on the fourth floor of Tower IV at the Urbana housing complex. That blaze was brought under control using the building’s internal fire-fighting system.