BANGKOK, March 30 (Xinhua) -- At least 20 Myanmar migrant workers were killed and three others wounded in a blaze onboard a bus in the northwestern Thai province of Tak in the wee hours on Friday, Thailand's Department of Disaster Prevention and Mitigation said.

The fire occurred at about 01:25 a.m. local time in the cargo bay of the bus, which was carrying a total of 47 Myanmar migrant workers.

The driver of the bus, cited by police, said he opened all doors of the bus when the fire occurred, yet still some 20 passengers did not make it out.

The 27 other migrant workers and the Thai bus driver and his wife managed to get off the burning bus, the police said.

The police are investigating the cause of the fatal incident.

The chartered bus had left Thailand's border district of Mae Sot at about 10:00 p.m. local time on Thursday and headed for Nava Nakorn industrial estate on the northern outskirts of Bangkok where the migrant workers have been employed.