SUWON, South Korea,  — 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.

Up 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 victims were all 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. and workers from Samsung’s subcontractor, named STI Service, 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.

Samsung officials said the leaked chemical was diluted but it was still strong enough to overcome the workers who had been exposed to it for a long time.

One worker collapsed at the scene and died later at a hospital in Seoul, police said, identifying him only by his surname, Park.

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 leak.

Samsung Electronics said in a statement that there is no possibility of the gas leaking outside of the plant but it did not explain why it had reported the leak to the police more than a full day later.

Nearly 30 hours after the leak, Samsung officials held a press briefing, during which they said they did not order some 50 workers at the plant to evacuate.

The provincial government of Gyeonggi, in which the Samsung plant is located, held an emergency meeting on Monday to deal with the apparent accident. Gyeonggi officials said.

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

The leaked gas sickened more than 3,000 villagers and withering hundreds of hectares of farmlands and orchards. The government designated the city as a special disaster zone.