SUWON (Yonhap News) -- Highly poisonous hydrofluoric acid gas leaked at the main plant of the world's largest memory chipmaker Samsung Electronics Co., killing one worker and injuring four others, police said Monday.

Some 2 to 10 liters of hydrofluoric acid, an acute poison that can damage lungs and bones and affect the nervous system, leaked from one of the pipes at the Samsung plant in Hwaseong, 60 kilometers south of Seoul, on Sunday, they said.

The leaks affected five subcontracted workers who were called in by Samsung Electronics to check and repair what appeared to be cracks in the pipe, police said.

The leak occurred around 1:30 p.m. Sunday and workers from Samsung's subcontractor, named STI, began repair work at 11:00 p.m., police said, quoting Samsung officials.

The repair work was finished at 4:46 a.m. Monday but all the five STI workers complained of pain in the neck and chest, they said, identifying the dead worker as a 34-year-old named Park.

Park, who apparently had been exposed to the poisonous gas for a long time, collapsed at the scene and died later at a hospital in Seoul, police said, adding that four others who had showed symptoms of dizziness had to receive treatment at a nearby hospital.

The medical condition of the four workers injured was not serious, as they have already left hospital, police said.

Police and fire officers said they were investigating the exact cause of the leaks.

Samsung Electronics said in a statement that there is no possibility of the gas leaking outside of the plant.

In a controversial move, however, Samsung reported the gas leak to the police and the provincial government of Gyeonggi, to which Hwaseong belongs, as many as 15 hours after the gas leak.

In September last year, some eight tons of hydrofluoric acid leaked from chemical maker Hube Globe in Gumi, some 260 kilometers southeast of Seoul, resulting in the deaths of five workers and injuries to 18 others.

The leaked gas caused massive damage, sickening more than 3,000 additional people and withering hundreds of hectares of farmlands and orchards, according to the authorities. To offer extra financial aid, the government designated the city as a special disaster zone.