An explosion at a chemical plant in South Korea has killed six workers, fire officials reportedly said. The blast took place Friday morning at the Hanwha Chemical Co. in Ulsan, about 180 miles southeast of Seoul.

According to reports, the explosion occurred when workers were welding the interior of a waste water storage facility. Fire authorities suspect that the gas trapped in storage area might have triggered the blast.

"Gas from the waste water, which had piled up inside the tank, was apparently ignited by the welding torch,” a fire official told Agence France-Presse.

About 30 emergency vehicles, along with 220 emergency workers, government officials, police and military personnel, were sent to the scene after the news of the incident, CNN reported, adding that one injured worker was taken to a nearby hospital.

An investigation into the cause of the explosion is reportedly underway.