20 people killed in South Korean battery plant explosion

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.

"Due to fears of additional explosions, it was difficult to enter," Kim said.

"As it is a lithium battery manufacturer, we determined that spraying water will not extinguish the fire, so we are currently using 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.

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.

'Mobilise all personnel'

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.

The president also warned authorities that they should "ensure the safety of firefighters considering the rapid spread of fire".

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

Authorities in Hwaseong sent out a series of alerts to residents warning them to stay inside.

"There is a lot of smoke due to factory fires. Please pay attention to safety, such as refraining from going out," one alert sent by text message said.

"Factory fire. Please detour to surrounding roads and nearby citizens please close windows," another one read.

South Korea is a major producer of batteries, including those used in electric vehicles.

Its battery makers supply EV makers around the world, including Tesla.

South Korea is also one of the world's largest producers of high-end semiconductors, and the government has invested heavily in key technologies including displays and batteries.