
Police said the accident happened just after 2am on Nakhon Sawan-Phitsanulok Road in tambon Nong Krood in Banphot Pisai district.
The driver was trapped inside the bus and drowned. The passengers escaped by breaking the windows.
A passenger, Yos Wannachon, said the bus left Nan at 5pm.
He said he felt the bus swaying briefly and then it crashed into a ditch in the middle of the road, flipped and crashed into the canal.
Police suspect that the driver fell asleep.