SEOUL - One worker was killed and five others injured in a South Korean explosion incident that happened in the country's southeastern city of Ulsan, Yonhap news agency reported on Friday.

The explosion occurred at around 2:35 pm local time (0535 GMT) at an Ulsan branch of the state-run Korea National Oil Corporation (KNOC).

When six workers affiliated with subcontractors of the KNOC were replacing decrepit oil pipelines, the explosion took place for an unidentified reason, the report said.

Police is investigation details.

Among the five workers injured, two are in critical conditions, according to Yonhap report.