At least 12 worshippers, including a child, were killed and 25 others injured when a suspected gas leak caused six air conditioners to explode almost simultaneously in a mosque on the outskirts of Bangladesh's capital Dhaka, fire officials said on Saturday.

The explosions took place during prayers at around 9pm at the Baitul Salat mosque, at the Narayanganj river port town on Friday.

Twenty-five worshippers sustained burn injuries in the blast, according to media reports.

While 11 worshippers died during treatment on Saturday, a boy succumbed to his injuries on Friday, said Dr Samantha Lal Sen, chief of state-run Dhaka Medical College Hospital's burn unit, the National Institute of Burn and Plastic Surgery.

He said 25 others are now being treated at the unit, but their condition was very critical as the burn caused more than 90 per cent damage to their bodies.

Almost all of them have inhalation burns, he said, adding that prime minister Sheikh Hasina called him this morning and expressed concern for the injured and directed to ensure all possible medical care for them.

Fire officials suspect accumulated gas from a leaking pipeline caused a fire that might have triggered the air conditioners to explode.

"A pipeline of Titas Gas passes beneath the mosque. We are suspecting that gas leaked from the pipeline and accumulated inside as the windows were closed. The explosion was probably triggered due to sparks when someone tried to switch on or off the ACs or fans," Narayanganj Fire Service's deputy assistant director Abdullah Al Arefin was quoted as saying by the Dhaka Tribune.

Witnesses said they found five to six people coming out of the mosque as soon as the blast occurred. Worshipers, most of them severely burnt, were found lying on the floor, the report said.

The Bangladesh Fire Service and Civil Defence, state gas transmission and distribution agency Titas and the district administration of Narayanganj each formed a committee to investigate the near-simultaneous explosions.