At least 12 dead and 39 injured in the blast at the nickel processing facility, highlighting dangerous working conditions.

The blast at the Chinese-funded Morowali Industrial Park on Sulawesi Island took place at 5:30am on Sunday while workers were conducting furnace repairs.

A spokesperson for the complex said those killed include seven Indonesians and five foreign workers, without stating their nationalities.

An initial investigation showed the explosion occurred when a flammable liquid ignited and the subsequent blast caused nearby oxygen tanks to explode as well, spokesperson Dedy Kurniawan said on Sunday.

The fire was successfully extinguished, according to the official.

The firm that runs the industrial park said it was “deeply saddened” by the disaster and said the remains of several identified victims had been flown home.

The island is a hub for the mineral-rich country’s production of nickel, a base metal used for electric vehicle batteries and stainless steel, and Beijing’s growing investment has stoked unrest over working conditions at its facilities.

In January, two workers, including a Chinese national, were killed at a nickel smelting plant in the same industrial park after a riot broke out during a protest over safety conditions and pay.