Thirteen workers were killed and 38 were injured on Sunday in the explosion of 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 blast occurred when workers repaired the furnace and installed plates at 5:30 a.m. on Sunday (2130 GMT on Saturday), killing eight Indonesian workers and five Chinese workers, Indonesia Morowali Industrial Park (IMIP) said in a statement. The fire was extinguished at 09:10 a.m. local time, it added.

“Based on initial investigations, the explosion (was) possibly caused because there was still some explosion-inducing liquid at the bottom of the furnace. During the repairing process, an explosion occurred,” an IMIP spokesperson said.

The first explosion triggered several other explosions because there were many oxygen cylinders used for welding and cutting furnace components for the repair, the spokesperson added.

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 monitoring of environmental standards.