The accident took place at about 9.30pm on the Bangkok-bound side of the highway in Sikhio district, reports the Bangkok Post.
From an initial police investigation, the Amnat Charoen-registered Toyota van, with the driver and 11 passengers on board. were heading from Amnat Charoen to Nakhon Pathom province.
While between kilometre markers 99-100, the van veered sideways, rammed into the metal railing and crashed into the ditch in the median strip. The LNG-powered van then went up in flames.
Nikom Sae Oun, leader of the Hook 31 rescue unit at Mo Chabok in Si Khiu district near the spot, said after hearing a loud explosion he rushed to the scene to find the van totally engulfed by fire. A passenger was seen slipping out of the van.
A fire engine soon arrived and put out the fire shortly afterwards. But 11 people, including the driver, were all burned to death in the van.
The passenger who managed to narrowly escape death was later identified as Thanachit Kingkaew, 20. He was admitted to Sikhio Hospital.
Governor Saksayam Sirimongkol was at the scene after the accident for inspection. He later went to the hospital to visit the survivor.