The explosion, which fire service officials suspect was caused by leakage from a pipeline, occurred on Friday night at a mosque in Narayanganj district just outside the capital, Dhaka.
A suspected gas explosion has torn through a Bangladesh mosque, killing at least 16 people and leaving several others with life-threatening burns, emergency services and police have said.
Worshippers were at Friday evening prayers when the blast sent a ball of flames through the mosque in the central district of Narayanganj, emergency services said.
Investigators suspected a spark from an air conditioner – which came on after a power cut – set off the gas.
"Leaked gas entered the mosque," Narayanganj fire chief Abdullah Al Arefin said on Saturday.
"When they shut the windows and doors and switched on the air conditioners there was an electricity spark that led to the explosion inside the mosque."
Fire officials said gas that accumulated in the mosque after pipeline leaks likely triggered the blasts.
"We primarily suspect that gas leaked from the pipeline and accumulated inside the mosque since the windows were shut. When the air conditioners was turned on, due to sparks the gas could have exploded," said Abdullah al Arefin, a senior fire service official.
All six air conditioners in the mosque exploded during the incident, he said.
Authorities have launched an investigation into the incident.
The 12 who died were among 37 taken to a specialist burns hospital in Dhaka in critical condition, said hospital spokesman Samanta Lal Sen.
He added that all had suffered 70 to 80 percent burns.
In Bangladesh, safety regulations are often flouted in construction. Hundreds are killed each year in fires in the nation of 168 million people.
In February last year, an inferno in Dhaka's old quarter killed 78 people.
One month later, 25 people were killed when a blaze engulfed a Dhaka office block.