Hundreds of Indonesian workers protested Wednesday against conditions at a Chinese-funded nickel-processing plant where an explosion killed at least 18 people and injured dozens more over the weekend.

The accident occurred on Saturday morning on Sulawesi Island as workers repaired a furnace at a plant owned by PT Indonesia Tsingshan Stainless Steel (ITSS) in the Morowali Industrial Park.

Sulawesi is a hub for the mineral-rich country's production of nickel, a base metal used in electric vehicle batteries and stainless steel, and China's growing investment in the sector has stoked unrest over pay and working conditions.

Images seen by AFP showed hundreds of workers taking part in the protest outside the complex.

Demonstrators gave a list of 23 demands to management, according to a letter sent to police by unions representing the workers. 

The demands included that smelters be better maintained, health clinics be improved to deal with emergencies, and Chinese workers be required to learn the Indonesian language.

"No production is worth a life!" protesters shouted through loudspeakers, video footage of the demonstration showed. 

Among those killed in the blast was Muhammad Taufik, a 40-year-old welder who left behind a wife and two children.

"The family is grieving, he was the breadwinner," Taufik's cousin Parlin Hidayat told AFP, adding that ITSS had given the family compensation worth 600 million rupiah ($30,625) after the accident.

"They hope there will be no more incidents like this in the future, let him be the last victim."

Thirty people are still being treated in hospital for their injuries after the blast, according to police.

Dedy Kurniawan, a spokesperson for Morowali Industrial Park, told AFP that the company had "done what they (the protesters) demanded two days ago," without specifying which demands had been met.

"We hope this demonstration will not continue after they hear our explanation," he said.

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.

In January, two workers, one of whom was 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.