Emergency personnel work at the site of a deadly fire at a lithium battery factory in Hwaseong, South Korea. Reuters

Twenty-two people were killed -- including 18 Chinese nationals -- in a massive fire at a South Korean lithium battery factory, the fire department said Monday, one of the country's worst factory disasters in years.

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

In the massive blaze that ensued, twenty-two people were killed, including 20 foreign nationals -- 18 Chinese, one from Laos, and one of unknown nationality, he said.

"Most of the bodies are badly burned so it will take some time to identify each one," he added.

Firefighters are still searching for one more person who remains unaccounted for, he said, adding that they had managed to contain the largest blaze at the plant and get inside.

Firefighters were "doing cooling operations to prevent the fire from expanding to nearby factories," Kim said.

Dozens of fire trucks were lined up outside the factory, an AFP reporter saw, with rescue workers carrying bodies, covered by blue blankets, out of the building on stretchers.

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.

Firefighters walk at the scene of a fire at a lithium battery factory on Monday. AFP

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.

"Due to fears of additional explosions, it was difficult to enter," Kim said, describing the tricky rescue operation.

"As it is a lithium battery manufacturer, we (had) determined that spraying water will not extinguish the fire, so we (used) dry sand," he added.

The lithium battery plant is owned by Aricell, a South Korean primary battery manufacturer. It is located in Hwaseong city, just south of the capital Seoul.

Shares of Aricell's parent company, S-connect, plunged by over 20 percent on the Seoul exchange by close Monday. S-connect owns 96 percent of Aricell.

Lithium batteries are used in everything from laptops to electric vehicles -- but can be highly explosive, with airlines, for example, imposing strict regulations on checking devices containing them.

Agence France-Presse