Two workers died and four others were injured Monday after a nitrogen leak at an LG Display factory north of Seoul, police and firefighters said.

The leak took place at around 12:50 p.m. at the P8 factory in Paju, about 40 kilometers north of Seoul. The workers from LG Display and its subcontractor were carrying out routine maintenance on the ninth floor when the valve of a nitrogen gas cylinder was presumably opened by mistake, firefighters said.

One worker died at the scene, with another being pronounced dead on his way to the hospital, authorities said.

The victims and the bodies were taken to four hospitals in the area, with one of the injured listed in serious condition, LG Display said. The victims were all in their 30s, according to South Korea's top maker of liquid crystal displays (LCD).

Police were investigating the exact cause of the accident, with more than a dozen firefighters remaining onsite to make sure there were no risks of another accident.

Shortly after the accident, LG Display offered an apology to the victims.

"We send our most heartfelt condolences and apologies to the deceased and will do everything in our power to help the injured recover as quickly as possible," the company said in a statement.

Monday's incident followed a similar nitrogen leak at the Shingori 3 nuclear reactor in Ulsan, some 410 kilometers southeast of Seoul, which killed three workers late last month.

Nitrogen makes up nearly 80 percent of the atmosphere, but can cause asphyxiation in the absence of oxygen. (Yonhap)