A fire broke out at a primary battery manufacturing plant, south of Seoul, on Monday, leaving at least one worker dead and three others injured, firefighters said, according to Yonhap News Agency.

The blaze started at lithium battery maker Aricell's plant in Hwaseong, 45 kilometers south of Seoul, at around 10:30 a.m., they said, noting firefighting was still under way as of the early afternoon.

The deceased worker was taken to a hospital after suffering cardiac arrest, while another was seriously injured and two sustained minor injuries, they said, adding at least 19 others are believed to be still stranded inside the plant.

"There are many people who remain out of contact. So it is expected that there will be more casualties," one firefighter said.

The fire reportedly occurred for unknown reasons at the three-story, reinforced concrete building with a total floor space of about 2,300 square meters.

Firefighters are reportedly having difficulties completely extinguishing the blaze because burning lithium batteries are difficult to handle by conventional fire extinguishing methods.