The massive explosion occurred on June 1 at about 4:30 am at a location just 15 kilometres across the Vietnam, Laos border from the from Cha Lo International Border Gate in Quang Binh Province, Vietnam.

Multiple social media posts show smoke coming out of the burned-out bus, which is standing in the middle of the road.

Initial reports indicate there were 12 casualties, with eight deaths and three seriously injured. The injured were evacuated to hospitals in Laos.

All of the casualties were riding on the bus.  No passers-by were apparently injured as a result of being close to the blast.

All of the eight deceased Vietnamese were from Nghe An Province. 

“When I arrive at the scene I see the bus going up in flames and fragments everywhere,” one eyewitness reported.

Laos police say the bus could have been blown up by an explosive device or targeted by a suicide bomber who detonated the device inside the bus.

Or it could have been caused by other as yet unidentified reasons. Authorities are continuing their investigation.