Several fatal accidents have caused concern about safety at Beijing's facilities on Sulawesi island AFP

At least 13 people were killed and 46 injured in eastern Indonesia on Sunday in an explosion at a Chinese-funded nickel-processing plant, the owner of the industrial park that hosts the facility 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 around 5:30 am (2130 GMT Saturday) at a plant owned by PT Indonesia Tsingshan Stainless Steel (ITSS) in the Morowali Industrial Park in Central Sulawesi province, a spokesperson for the complex said in a statement.

"The confirmed number of fatalities is 13 people, consisting of nine Indonesian workers and four workers from China," the spokesperson said in a statement, revising the number of the fallen foreign workers down one to four.

Forty-six other victims were injured, mostly due to exposure to hot steam, he said.

About 29 victims were referred to a government-run hospital in Morowali district, while 12 others were under observation at a clinic in the industrial complex and five people were receiving outpatient care.

An investigation showed the explosion happened during repair work on a furnace, which was closed for maintenance, when residual slag from the furnace flowed out and came in contact with flammable materials around the location.

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

Tsingshan Holding Group, the world's biggest nickel producer and China's biggest stainless steelmaker, holds a majority stake in ITSS.

ITSS is a tenant in the industrial park, which is also majority owned by Tsingshan along with local partner Bintang Delapan.

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, while the remains of one victim have been handed over to the family.

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.

Acting Morowali district head Rachmansyah Ismail earlier told broadcaster Kompas TV that as of Sunday afternoon 25 of the injured -- 15 Indonesians and 10 foreign nationals -- had been immediately rushed to hospital after the blast.

Seventeen were seriously injured while eight suffered moderate injuries, he said.

The manpower ministry will deploy a team tomorrow to investigate the accident, said ministry official Yuli Adiratna.

He said the ministry was probing the operations of the company.

"We are still gathering information and accurate data from the field on whether to stop the company's activities or not," Adiratna told AFP.

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 where the riot and fire took place is operated by PT Gunbuster Nickel Industry (GNI), a local unit of China's Jiangsu Delong Nickel Industry.