An underground gas pipeline near a mosque exploded during evening prayers outside the capital of Bangladesh, killing 24 Muslim worshippers and leaving dozens with life-threatening burns, officials said Saturday.

The blast occurred Friday night as people were finishing their prayers at Baitus Salat Jame Mosque at Narayanganj, local police chief Zayedul Alam 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 told Agence France-Presse (AFP).

"When they shut the windows and doors and switched on the air conditioners there was an electric spark that led to the explosion inside the mosque."

The 24 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% burns.

Police said at least 45 people were injured by the blast and that people had spoken of smelling a gas leak.

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.

TV stations reported that because of the impact of the gas line blast, at least six air conditioners also exploded inside the mosque. Firefighters were investigating why the explosions took place.