JAKARTA: At least 12 people were killed and 39 injured in eastern Indonesia on Sunday after an explosion at a Chinese-funded nickel-processing plant, an industrial park official said.

The accident took place around 5:30 am (2130 GMT Saturday) at a plant owned by PT Indonesia Tsingshan Stainless Steel in the Morowali Industrial Park located in Central Sulawesi province, a spokesperson for the complex said in a statement.

"The current number of victims is 51 people. 12 people died in the incident. 39 people with minor and serious injuries are currently receiving medical treatment," spokesperson Dedy Kurniawan said.

The statement said seven Indonesians and five foreign workers were killed, without identifying their nationalities.

An initial investigation showed the explosion happened during repair work on a furnace when a flammable liquid ignited and the subsequent blast caused nearby oxygen tanks to explode as well, the official said.

The fire was successfully extinguished on Sunday morning, according to the statement.

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.