Four coal miners suffered critical burn injuries Monday in the northern province of Thai Nguyen after a methane explosion in the mine they were working in.
The victims, between 24 to 34 years of age, were admitted to hospital in critical condition.
Doctor Nguyen Cong Bang of the Thai Nguyen Central General Hospital said one miner suffered almost 100 percent burns, two others 90 percent and the last one 70 percent.
The victims have been sent to the National Burns Institute.
According to first investigation, the victims were mining for coal more than 10 meters underground when methane gas set off a fire.
The mining was illegal, investigators said.
The police are investigating the accident.