At least eleven people were killed and three remain missing after a fire tore through an auto parts factory in Daejeon, South Korea on Friday, officials said.

"We understand that 11 are dead, 25 are seriously injured," an official from the interior ministry's department that handles fires and other disasters told AFP news agency.

"We also understand that 34 have been injured but not in a serious condition and three are still missing," he added.

The fire broke out around 1:00 p.m. (0400 GMT) and spread rapidly through the facility, sending thick gray smoke billowing into the sky.

Some 170 workers were in the building at the time. Images from the scene showed workers leaping from upper floors to escape the flames.

The cause was not immediately known, said Nam Deuk-woo, fire chief of Daedeok District, though witnesses reported an explosion.

Firefighters hindered by risk of building collapse

Firefighters could not enter parts of the building in South Korea's fifth-largest city because of fears it might collapse.

Crews, instead, focused on preventing the blaze from spreading to nearby facilities and removing hazardous chemicals.

Officials said about 200 kilograms (440 pounds) of highly reactive chemicals are stored in the facility.

South Korea's Yonhap news agency said the site stored sodium, which can explode if improperly handled.

Some of the injured suffered smoke inhalation, while others were hurt after jumping from the building, Nam said.

President orders full-scale rescue

The fire prompted South Korean President Lee Jae Myung to order the full mobilization of personnel and equipment to support rescue efforts.

More than 500 emergency personnel and about 120 vehicles were deployed, including evacuation aircraft, an unmanned water cannon vehicle and firefighting robots designed to operate in hazardous areas.

The robots were used to cool the structure and conduct a safety inspection, allowing searches for the missing workers late on Friday.

One person's remains were found on the second floor,  while nine others were discovered in what is believed to have been a gym on the third floor, Nam said.

By Saturday morning, rescuers had searched all accessible areas of the plant, he said, adding that the remaining missing were likely trapped beneath collapsed rubble.

The fire was extinguished by Saturday afternoon.

Edited by: Kieran Burke