The blast at Morowali industrial park on Sulawesi Island took place during furnace maintenance at around 5.30am local time.

About 38 people were taken to hospital, police said, some in a critical condition.

At least five Chinese and eight Indonesian workers died when the furnace suddenly exploded while they were repairing it, Central Sulawesi police chief Agus Nugroho said.

The blast was so powerful it demolished the furnace and damaged parts of the side walls of the building, he added.

Authorities are working to determine whether negligence by the company led to the deaths, the police chief said.

The explosion is the latest in a series of deadly accidents at Chinese-owned nickel smelting plants in Indonesia.

Nickel has become increasingly crucial for 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.

Nickel is a key component in global battery production for electric vehicles.

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The accident happened at PT Indonesia Tsingshan Stainless Steel.

"We sincerely apologise for this incident and we are working closely with authorities to investigate what caused the accident," company spokesperson Deddy Kurniawan said.

Rescuers extinguished the fire and evacuated workers after a nearly four-hour operation, he added.

A preliminary investigation showed there were explosive liquids at the bottom of the furnace that triggered a fire and explosion in nearby oxygen cylinders.