This photo provided by fire authorities in Ulsan shows blaze engulfing a plant of S-Oil, July 28. Yonhap

A fire at a plant of S-Oil, a major refiner, was completely extinguished Sunday, about five hours after it started, according to firefighters.

No casualties were reported as the fire erupted at 4:47 a.m., with photos showing dense flames rising from the plant. Fifty-six vehicles and some 300 personnel were mobilized to extinguish the blaze.

The fire is presumed to have broken out in a heating facility used to produce xylene.

Fire authorities are investigating the exact cause and scope of the damage. No harmful substance has been detected in the area following the fire.

The S-Oil plant is located in Ulsan, some 300 kilometers southeast of Seoul. (Yonhap)