Around 20 bodies have been found at a South Korean lithium battery factory after a massive blaze on Monday, the Yonhap News Agency said, with firefighters saying they were still searching the building.

Over 100 people were working in the factory when workers heard a series of explosions from the second floor, where lithium-ion batteries are inspected and packaged, firefighter Kim Jin-young told media.

Some 78 people were confirmed safe but many more were still missing, with Yonhap saying that “about 20 bodies (were) found” at the site, after rescue workers finally managed to get inside.

Kim told media that they had managed to put out the largest fire at the factory and were pulling bodies out of the charred building.

“A rescue team has gone inside and is carrying out search and rescue operations,” he said.

Images shared by Yonhap after the fire broke out showed huge plumes of billowing grey smoke rising into the sky above the factory, with orange flames inside the building. Dozens of fire engines were seen outside.

The vast factory had an estimated 35,000 battery cells on the second floor in storage, with more batteries stored in other areas.

Lithium batteries burn hot and fast, and are difficult to control with conventional fire extinguishing methods.