At least 49 people have died after a fire that sparked a huge chemical explosion and was still blazing on Sunday at a shipping container depot in Bangladesh, officials said.

The toll was expected to rise with over 300 people injured, some of them seriously, and eyewitnesses said they had seen unrecovered bodies in the facility near the major southern port of Chittagong.

Several hundred rescuers were battling the blaze that broke out late Saturday in Sitakunda, about 40 kilometres (25 miles) from Chittagong, when a number of containers holding chemicals exploded, the fire brigade told reporters.

"The death toll from the fire has risen to 49," Elias Chowdhury, chief doctor of the region, told AFP as firefighters continued to battle the blaze. "More than 300 people are injured."

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

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

The injured include at least 40 firefighters and 10 police officers, Chittagong regional police chief Anwar Hossain told AFP. At least five firefighters were among those killed.

"The number of fatalities is expected to rise as some of the injured are in critical condition," Hossain said.

Eyewitnesses said that the blast engulfed people who had been battling the fire.

"I was standing inside the depot. The explosion just threw me some 10 metres (yards) from where I was standing. My hands and legs are burnt," lorry driver Tofael Ahmed said.   

The explosion was so loud that it shook residential buildings several kilometres from the depot, said Mohammad Ali, 60, who has a nearby grocery store.

"A cylinder flew around half a kilometre from the fire spot to our small pond when the explosion occurred," he said. 

"The explosion sent fireballs in the sky. Fireballs were falling like rain. We were so afraid we immediately left our home to find refuge... We thought the fire would spread to our locality as it is very densely populated," he said. 

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.

Chowdhury, the chief doctor in Chittagong, said the injured had been rushed to different hospitals in the region as doctors were brought back from holiday to help.

Requests for blood donations for the injured flooded social media. 

Emergency crews were still working to put out the fire Sunday morning and military clinics were helping to treat the injured.

Mominur Rahman, chief administrator of Chittagong district, said the government has deployed some 200 army troops to the depot to prevent chemicals flowing into the sea.

He said while the fire was largely under control, there were "still several pockets of fire". 

"Firefighters are trying to control these pockets of fires. The fire has spread to at least seven acres of land inside the depot," he said. 

Rahman said a probe has been ordered.

He added that the depot contained millions of dollars of garments waiting to be exported to Western retailers, for whom Bangladesh is a key supplier.

Ruhul Amin Sikder, spokesman for the Bangladesh Inland Container Association (BICA), said some of the containers at the 30-acre private depot contained chemicals, including hydrogen peroxide.

The director of the B.M. Container Depot, Mujibur Rahman, said the fire's cause was still unknown. He added the facility employs about 600 people.

Fires are common in Bangladesh due to lax enforcement of safety rules. In July 2021, 54 people died when a blaze ripped through a massive food-processing factory outside the capital Dhaka. 

In February 2020, 70 people were killed when another fire engulfed several Dhaka apartment blocks.