Several individuals sustained injuries and at least six people were killed on Saturday when a fire started at an oxygen facility in southeast Bangladesh after an explosion.

Officials say that the number of fatalities may increase given that a rescue effort is currently taking place at the facility at Sitakunda, 40 kilometers (25 miles) southeast of the port city of Chittagong.

According to a fire department officer, the reason of the explosion was not immediately apparent.

“Six bodies were recovered from the site,” local government official Shahadat Hossain told Reuters, adding a rescue operation was continuing.

A huge bang was heard which shook an area with a radius of up to two kilometers, police official Nayhanul Bari said, quoting witnesses.

A massive fire at a container depot in the area killed 50 people and injured nearly 200 in June last year.