Thirteen workers were killed and 46 injured on Sunday in a fire at a nickel smelter furnace owned by Indonesia Tsingshan Stainless Steel (ITSS) on Sulawesi island, the owner of the industrial park where the smelter is located said.

The fire occurred when workers repaired the furnace and installed plates at 5:30 a.m. on Sunday (2130 GMT on Saturday), killing nine Indonesian workers and four Chinese workers, Indonesia Morowali Industrial Park (IMIP) said in a statement. The fire was extinguished at 9:10 a.m. local time, it added.

It had said earlier that an explosion killed eight Indonesian and five Chinese workers.

The furnace was shut off the day before to prepare for maintenance, IMIP said, but during the maintenance process excess iron slag flowed from the furnace.

"The furnace walls then collapsed and the remaining iron slag flowed out, causing a fire and resulting in some workers at the location suffering injuries and even fatalities," IMIP spokesperson Dedy Kurniawan said in the statement.

The workers were injured by hot steam from stainless steel slag and the burning fire, Dedy told a separate interview with local station Metro TV.

There was no explosion or oxygen canister on site, he said, revising the company's earlier statement.

IMIP is a nickel-focused industrial park owned by China's Tsingshan and its local partner Bintang Delapan Group, which produce stainless steel and carbon steel. ITSS is one of the tenants at the industrial park, IMIP said.

IMIP will coordinate with related parties to investigate the incident and cover all treatment costs for victims, the company said.

Nickel has become increasingly crucial for resource-rich Indonesia, the world's biggest nickel producer, with billions of dollars of global investment flowing in after the government banned exports of unprocessed ore in 2020.

Southeast Asia's biggest economy is trying develop downstream nickel industries and lure big-ticket investment from manufacturers of electric vehicles and their batteries.

However, several fatal accidents have occurred in Indonesia's nickel processing industry in recent years. President Joko Widodo is keen to develop the sector but has also called for improvements in safety and has pledged to enhance the monitoring of environmental standards.

(Reporting by Bernadette Christina in Jakarta; Editing by William Mallard, Jamie Freed, Kirsten Donovan)