At least 49 people have been killed and more than 300 injured after a massive fire swept through a container depot in southeastern Bangladesh, according to senior officials.

The fire broke out at a container facility on Saturday night at Sitakunda, 40km (25 miles) from the port city of Chittagong, triggering multiple explosions, officials said.

"The death toll has risen to 49,” Elias Chowdhury, Chittagong’s chief doctor, told Al Jazeera. He added that more than 300 people have been injured in the blaze and subsequent explosions.

"The number of fatalities is expected to rise as some of the injured are in critical condition,” Chowdhury earlier told the AFP news agency.

Six firefighters are among those killed, Brig General MD Main Uddin, director general of Fire Service and Civil Defence, told Al Jazeera.

At least 21 firefighters, who had been at the scene attempting to douse the blaze, have been injured.

They were hurt during the secondary explosions.

What caused the blaze?

The explosions shook the neighbourhood and shattered windowpanes of nearby houses, local residents said.

"I was standing inside the depot. The explosion just threw me some 10 metres [11 yards] from where I was standing. My hands and legs are burned,” Tofael Ahmed, a truck driver, 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.

irefighters were still working to put out the fire on Sunday morning, police said.

Mohammed Manzurul Islam from the Bangladesh Red Crescent Society told Al Jazeera the cause of the fire was a container full of the hydrogen peroxide chemical, which spread to other containers including one that was holding garments.

"The problem is that the firefighters [who arrived first at the scene] didn’t know there was a chemical,” he said, speaking from Dhaka. "They thought it was a small fire. What I heard from our colleagues was that the sound of the explosion was heard from two to three miles.”

At least 25 fire brigades fought for 18 hours to battle the explosion, he continued.

"The firefighters are afraid that if there is more chemicals there will be more explosions,” Manzurul Islam added.

Al Jazeera’s Tanvir Chaudhury, reporting from Dhaka, said efforts were on to avoid the explosion of containers containing chemical substances.

"Many of the containers have fumes coming out of them,” he said. "Firefighters are worried that if there are chemicals in any of those containers that could be a clear danger to the neighbourhood and the public.”

"The special unit of Bangladesh’s military is helping the firefighters to salvage the operation,” he continued. "There’s a lot of chemicals on the ground, and people are saying they are having breathing problems.”

About 5,000 containers are at the BM Inland Container Depot, which handles goods for export and import, according to local media.

Chaudhury said security measures at industrial facilities have improved since the Rana Plaza disaster in 2013, but that chemical plants located in close proximity to towns still posed a risk for residents as well as workers.

Chittagong civil surgeon Mohammed Elias Hossain has urged all doctors in the district to help tackle the situation and called for emergency blood donations.