Explosion at a chemical plant in South Korea kills 5 workers, 1 missing

A distorted waste storage facility is seen after an explosion at a chemical plant run by Hanwha Chemical Co. in Ulsan, South Korea, Friday, July 3, 2015. (Kim Yong-tae/Yonhap via AP) KOREA OUT (The Associated Press)

Firefighters pull up the body of a worker from debris after an explosion at a waste storage facility at a chemical plant run by Hanwha Chemical Co. in Ulsan, South Korea, Friday, July 3, 2015. (Kim Yong-tae/Yonhap via AP) KOREA OUT (The Associated Press)

Fire officials say an explosion at a chemical plant in South Korea has killed five workers. Another person is missing.

The officials say the blast occurred Friday at a waste storage facility belonging to a chemical plant run by Hanwha Chemical Co. in the southeastern city of Ulsan.

The exact cause of the explosion wasn't immediately known. But fire authorities suspect that gas trapped in the storage area might have triggered the blast.

The fire officials in Uslan say the victims were doing welding work when the explosion happened.

The officials spoke on condition of anonymity because they were not authorized to speak to the media about the explosion.