At least 56 people in the southern city of Seosan were injured Wednesday following an explosion at Lotte Chemical Corp.'s plant.

Four company employees and residents were among those injured, Lotte said, adding that two of them have been hospitalized with serious burns. No deaths have been reported.

"We are truly sorry for causing big concern among the public," Lotte Chemical CEO Lim Byung-yun said in a news conference. He said the company is doing its best to clean up the scene and come up with compensation measures.

The fire broke out following an explosion at 2:59 a.m. at the naphtha cracking center in Daesan petrochemical complexm in Seosan, some 120 kilometers south of Seoul, according to fire officials.

The naphtha cracking plant produces ethylene, propylene and other petrochemical feedstocks.

The fire was mostly put out by 5:12 a.m., after more than 270 firefighters and 66 vehicles were mobilized in a major fire response.

Lotte Chemical said the explosion occurred while compressing naphtha, adding there was no risk of a toxic chemical leak or an additional explosion.

"We are investigating the exact cause based on the company's explanation that the explosion occurred during the compression process," a fire official said. The police have also set up a team to probe the case.

Lotte Chemical said it has suspended nine of its 13 facilities following the fire.

Sales from the Seosan plant account for 21.8 percent of Lotte Chemical's total sales, according to a regulatory filing. The company plans to post another regulatory filing once the scope of the damage is confirmed. (Yonhap)