At least one person has been killed while 21 others are "unaccounted for" following a major fire that broke out at a lithium battery factory in South Korea on Monday as the blaze continued to rage, authorities said.

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

"We are still unable to go inside and carry out rescue operation. We will carry it out once we get the fire under control," fire fighter Kim Jin-young told media.

"Twenty-one workers are unaccounted for now. We are planning to track their whereabouts with their contacts provided from the company," Kim added.

One person was killed, and another had sustained serious burns, he added.

Images shared by the Yonhap news agency 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.

South Korea's President Yoon Suk Yeol issued emergency instructions to authorities, telling them to "mobilise all available personnel and equipment to focus on searching for and rescuing people," his office said.

He also warned authorities that they should "ensure the safety of fire fighters considering the rapid spread of fire".

Firefighting and rescue efforts were ongoing, but the cause of the fire remains unknown.

South Korea is a major producer of batteries, including those used in electric vehicles. Its battery makers supply electric vehicle makers around the world, including Elon Musk's Tesla.