A pickup truck plunged off the end of a collapsed bridge during heavy rain in the early hours of the morning in Tak province on Wednesday.
The 50-year-old driver was later found with serious injuries and was rushed to Umphang Hospital.
The bridge spans a large creek in tambon Mo Kro on the road to Mae Sot.
The area had been hit by continuous rain during the preceding days and the rain-swollen creek had eroded away the bridge support, causing a section of it to collapse.
The bridge was shrouded by heavy rain and in the darkness the truck was believed to have run off the broken end about 3am, falling about 5 metres. The driver was seriously injured when found by rescue workers and was rushed to hospital.
Traffic along the road was stopped by the broken bridge and the accident. Ambulances taking patients to a hospital in Mae Sot were held up, along with 10 buses with more than 200 tourists.
Road repair teams were at the scene.