Three workers died at a Hyundai car factory on Tuesday, the South Korean carmaker told AFP, with local reports suggesting it was an accident during a vehicle performance test.

Along with its affiliate Kia, Hyundai is the world’s third-largest automaker, with over 4.2 million units in global sales in 2023.

“Three researchers died on an Ulsan assembly line,” a Hyundai representative told AFP.

“We are trying to determine the cause of the incident,” the representative said, without providing further details.

Hyundai’s Ulsan plant is 370 kilometers (229 miles) southeast of Seoul, and the assembly line there has been described by the company as “the world’s largest car factory” with an export shipping dock .

According to South Korea’s Yonhap news agency, the incident occurred during a performance test of the vehicle inside a chamber.

Unvented exhaust gases from inside the room may have been responsible for the fatal accident, Yonhap said.

“The three — two Hyundai researchers and the other affiliated with a subcontractor — were found collapsed in a factory test room where they were conducting a performance test of the car,” Yonhap reported.

“They were taken to nearby hospitals but were declared brought dead,” it said.

“The victims were believed to have suffocated due to toxic gases in the confined space and a police investigation is ongoing to determine the exact cause of the accident.”

In a statement to AFP, Hyundai said it was “deeply saddened by the incident that took place” at the plant and pledged to cooperate fully with investigators.

“We will cooperate fully with all relevant authorities to determine the cause of this incident as more information becomes available,” the automaker said.

She added that she “will work tirelessly to implement measures to prevent any future incidents,” the statement said, which did not include details of the incident.

Hyundai and Kia together account for about 80 percent of all new vehicle sales in South Korea’s domestic market, according to 2023 data.

A worker died at the same Hyundai Motor plant in Ulsan in 2023 after his head was caught in a heat treatment machine during an inspection, local media reported at the time.

The 2023 incident prompted Hyundai to issue an apology, saying it would “do its best to come up with follow-up measures” to prevent such incidents.

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