Officials fear the casualty count may rise, as an estimated 23 people, including 20 foreign nationals and two Koreans, are believed to be trapped inside the facility.
The blaze started at 10:31 a.m. at a factory operated by Aricell in Hwaseong, Gyeonggi Province. The cause of the fire remains unknown.
"We expect the number of casualties to increase, as many people remain unaccounted for," a fire department official told reporters at the scene.
A witness claimed explosive combustion occurred in a battery cell during the fire.
The three-story concrete building houses operations for manufacturing primary batteries using lithium.
The fire department mobilized 145 personnel and 50 pieces of equipment, including fire engines. Firefighting efforts have been complicated by the presence of hazardous chemicals such as lithium, officials said.
