Both the drivers of the Bangkok-Si Sa Ket bus and the truck were killed. Ten people died at the scene and another at Sangha district hospital, police said.
The accident happened at 3.40am on the Chokechai-Dejudom Road in Tambon Sakad of Sangha district.
Police quoted survivors as saying that the bus driver was trying to overtake a vehicle but failed so cut into the lane of the incoming truck and the two vehicles collided.
The bus left Morchit Bus Terminal at 8.30pm, heading to Si Sa Ket while the truck was heading to Nakhon Ratchasima.
Rescuers had to use iron cutters to free many bus passengers trapped inside the bus wreckage.
The injured were rushed to several district hospitals – Sangha, Lamduan and Prasat while seven victims, who were severely injured, were sent to Surin Hospital.
The overturned bus’s NGV gas tank also leaked, prompting rescuers to douse it with water to prevent it from catching fire.
The accident caused traffic congestion on the road for over two hours.
The bodies of the 11 victims are being kept at Sangha hospital pending autopsy and subsequent claiming by relatives.