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 island of Sulawesi 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.
The accident occurred at around 5:30 am (2130 GMT Saturday) at a plant owned by PT Indonesia Tsingshan Stainless Steel in the Morowali Industrial Park 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. There are 39 people with minor and serious injuries who are currently receiving medical treatment," spokesperson Dedy Kurniawan said.
The statement said seven Indonesians and five foreign workers were killed.
Kurniawan told AFP all five foreign workers were Chinese nationals.
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 extinguished Sunday morning, according to the statement.
The firm that runs the industrial park said it was "deeply saddened by this disaster, particularly for the families affected".
It said the remains of several identified victims had been flown home.
Footage shared with AFP showed plumes of smoke emerging from the facility with emergency services at the scene and workers looking on.
A photo shared with AFP showed the bodies of the victims lined up on top of orange body bags in a room in one of the clinics at the industrial complex.
"Their faces were burnt, their clothes were all burnt," a worker at the industrial complex told AFP on condition of anonymity.
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.
Deadly fires are not uncommon in Indonesia, a sprawling country of more than 250 million people where safety regulations are often flouted.
In June a fire at the same plant left one dead and six others injured, in another incident that has stoked concern over safety at facilities funded and operated by Chinese companies.
The facility is operated by PT Gunbuster Nickel Industry (GNI), a local unit of China's Jiangsu Delong Nickel Industry.
