South Korean authorities have ordered workers off one of petrochemical company Yeochun NCC's (YNCC) naphtha crackers in the city of Yeosu after a blast killed four people and injured four.

The incident at YNCC's third plant in Yeosu comes as businesses brace for greater scrutiny under a new South Korean law punishing management for incidents involving worker death.

The regional office of South Korea's labour ministry told Reuters that the ministry ordered workers to halt work at the entire third plant.

"There is no disruption in production, but we have entirely halted maintenance and repair work," an official at YNCC told Reuters.

YNCC's first and second plants are also operating, the YNCC official said, adding that the blast occurred during a leak test in a cleaning process that is a procedural operation carried out every four years.

YNCC's third naphtha cracker in Yeosu, the site of the explosion, produces 470,000 tpy of ethylene.

YNCC's first and second naphtha crackers in Yeosu produce 900,000 and about 920,000 tpy of ethylene each.

YNCC's entire capacity is 2.29 MMtpy, about 1.1% of global capacity, Samsung Securities analyst Cho Hyun-ryul said.

"If the impact is limited to the incident site, supply disruption will not be significant," he said.

"However, a suspension order for the entire production cannot be ruled out, as stricter rules are imposed on work sites since... the Severe Accident Punishment Act. If so, this could affect not just 470,000 but 2.29 MMt."

The new South Korean law, which took effect late last month, imposes criminal punishment of one or more years of jail or fines up to 1 B won ($834,028) for severe industrial accidents on business owners and responsible management, if they violated a duty of safety measures stipulated in the law.

(Reporting by Heekyong Yang & Joyce Lee; Editing by Muralikumar Anantharaman, Gerry Doyle and Raju