A furnace explosion at a Chinese-owned nickel factory in Indonesia on Sunday has killed at least 13 workers and injured 38 others, officials say.

The incident took place at a factory in the Morowali Industrial Park on the island of Sulawesi.

The factory is operated by Chinese steel and nickel giant Tsingshan, which has stakes in Indonesia’s lucrative nickel mining industry and runs operations under its local arm, Indonesia Tsingshan Stainless Steel (ITSS).

In videos, thick black smoke from huge fires can be seeing rising in the air.

Among the workers killed were eight Indonesians and five Chinese, Reuters reported.

The blast was said to have occurred when workers were repairing a furnace. “During the repairs process, an explosion occurred. Based on initial investigations, it (was) possibly caused because there was still some explosion-inducing liquid at the bottom of the furnace,” read a statement issued by the company and reported by Reuters.

Several oxygen cylinders nearby also exploded, which fueled the fires, said Hamid.

Indonesia is the world’s largest exporter of nickel and is also rich in copper, cobalt and bauxite, used in the making of electric vehicle (EV) batteries. As demand for EVs surges around the world, Indonesia has emerged as a global leader in nickel production and has been aggressive courting foreign investment in smelters and processing plants from countries like China with its EV-friendly business policies.

But critics say the government’s rush to expand its nickel processing and EV market has come at a cost to the environment as well as people like farmers and indigenous tribes.

Indonesian politician and labor activist Said Iqbal called for an investigation by the Indonesian Manpower Ministry. “The (operator) must bear the costs of medical treatment and accident compensation for those affected,” he said in a statement.

“There must also be heavy sanctions for those who violate regulations,” he added.