At least two people have been killed and six severely injured in an explosion and fire at the biggest production site in Germany belonging to chemicals maker, BASF.

Two people are still missing, BASF said.

The explosion occurred on a supply line connecting a harbour and a tank depot on the Ludwigshafen site on Monday morning, according to BASF, the world’s biggest chemicals company.

A fire that broke out following the blast sent up plumes of smoke for hours, prompting BASF and the city of Ludwigshafen to urge residents in the surrounding area to avoid going outside and to keep their windows and doors shut.

Flames at the BASF site in Ludwigshafen, Germany. Photo: Getty.,

Measurements taken in the area so far have indicated no risk from toxic fumes, BASF said.

“We deeply regret that employees died and several people were injured. Our sympathy is with the affected people and their families,” the Ludwigshafen site’s chief, Uwe Liebelt, said in a statement.

The company said it was unclear so far what caused the explosion. BASF also said it could not say what financial impact the explosion might have.

It shut down 14 facilities, including its two steam crackers, large units that make basic chemical components, for safety reasons and because the supply of raw materials was disrupted by the blast.

The Ludwigshafen site, around 80km south of Frankfurt, is the world’s largest chemical complex, covering an area of 10sq km and employing 39,000 workers, according to BASF.

It is located on the Rhine River and receives many of its raw materials by ship.

The harbour at which the explosion occurred is a terminal for combustible fluids such as naphtha and methanol that are important for BASF’s supply of raw materials.

News of the explosion came less than two hours after BASF said four people were injured in a gas explosion at its Lampertheim facility, a plant near Ludwigshafen that makes additives for plastics.

An aerial view of the fire