Updated 8.02pm

At least two people died and six were severely injured today in an explosion and fire at chemicals maker BASF's biggest production site in Germany, the company said.

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 at around 1120 local time (0920 GMT), according to BASF, the world's biggest chemicals company.

Photo: Reuters/Ralph Orlowski

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.

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 80 kilometres (50 miles) south of Frankfurt, is the world's largest chemical complex, covering an area of 10 square kilometres (four square miles) 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.