Five people have died and two others were injured on Monday after an explosion and fire on a South Korean production line for rocket propellant at a factory operated by Hanwha Aerospace in the city of Daejeon, officials said.

The two survivors, including one who was badly burned, had escaped from the facility themselves, a fire official told a briefing.

“Authorities have yet to identify the victims because their bodies were severely damaged,” a health official told the same briefing.

A fire official said that an explosion had triggered the blaze, though the cause of the blast was still being investigated. The blast appeared to have occurred while water was being used to clean explosive material from tools making rocket propellant, a Hanwha official told a company briefing.

“We bow our heads in apology to the victims and their bereaved families,” said Chief Executive Officer Son Jae-il, pledging to cooperate fully with authorities to determine the cause of the accident.

The five dead included two temporary workers in their 20s and all were employed by Hanwha, the company said.