HWASEONG, South Korea, June 24 (Reuters) - A lithium battery factory in South Korea was set on fire after multiple batteries exploded on Monday, killing 22 workers, most of them Chinese nationals, fire officials said.

The fire and a series of explosions ripped through the factory run by primary battery manufacturer Aricell in Hwaseong, an industrial cluster southwest of the capital Seoul.

The victims likely succumbed to extremely toxic gas within seconds of the blaze getting out of control, the officials said. It was unclear what caused the explosions and the fire was largely extinguished in about six hours.

Eighteen Chinese workers, two South Koreans and one Laotian were among the dead. The nationality of the other deceased worker was yet to be confirmed, Kim Jin-young, an official at the Hwaseong fire service, told reporters, citing information from company officials.

The blaze was first reported at 10:31 a.m. (0131 GMT) after a series of battery cells exploded inside a warehouse of 35,000 batteries, Kim said.

A Reuters journalist saw firefighters moving up to six bodies out of the factory. Due to the intensity of the blaze, rescuers were finding it difficult to identify the dead, Kim said.

Two people were being treated for major burns, officials at the scene said.

Live TV footage showed firefighters spraying the damaged steel and concrete building. Parts of the upper level had collapsed, and large chunks of the building looked like they had been blown out into the street by explosions.

Aerial footage showed massive white smoke clouds billowing from the structure and explosions rolling through the building.

Gyeonggi province fire official Cho Sun-ho said most of the foreign workers killed were temporary hires, likely unfamiliar with the structure of the building. Smoke and the fire blaze spread within 15 seconds and the victims likely succumbed after taking one or two breaths, he said.