At least 49 people died and hundreds were injured after a fire sparked a huge chemical explosion at a shipping container depot in Bangladesh, officials said on Sunday.

The toll was expected to rise, with some of the more than 300 people injured in serious condition, officials said, while volunteers reported that there were more bodies inside the smouldering, wreckage-strewn facility.

The fire started late on Saturday at the depot in Sitakunda, which stores around 4,000 containers, many filled with garments destined for Western retailers. The facility is about 40 kilometres (25 miles) from the major southern port of Chittagong.

The blaze caused containers holding chemicals to explode, engulfing firefighters, volunteers and journalists in an inferno, hurtling people and debris through the air, and turning the night sky a blazing orange.

Buildings located kilometres away rattled with the force of the blast.

Elias Chowdhury, regional chief doctor, told AFP that the number of dead was 49 but would likely increase.

"The death toll will rise as the rescue work has not been completed yet," Chowdhury said.

"These people -- including several journalists who were doing Facebook lives -- are still not accounted for."

Firefighters continued to douse pockets of fire on Sunday afternoon, with television footage showing smoke still billowing from some containers, more than 19 hours after the fire began.

Reazul Karim, operations director of the fire department, said that at least seven firefighters died and at least four others were missing.

"Never in our fire department history have we lost so many firefighters in a single incident," Bharat Chandra, a former senior firefighter, told AFP.

"There are still some bodies inside the fire-affected places. I saw eight or 10 bodies," one volunteer told reporters.

Mujibur Rahman, the director of B.M. Container Depot, the firm operating the facility with around 600 workers, said that the cause of the initial fire was still unknown.

The container depot held hydrogen peroxide, fire service chief Brigadier General Main Uddin told reporters.

"We still could not control the fire because of the existence of this chemical," he said.