Thirty-one passengers were injured, two critically, when a Nong Khai-Rayong bus overturned in Nakhon Ratchasima early Wednesday morning.

Police and rescue workers were summoned at 2.40am to the scene on Mitraparp Highway in Ban Don Tabaeng, Noen Sung district.

The blue-and-white air-conditioned bus was carrying 41 passengers.

Police suspect that the driver, whose name was withheld, dozed off behind the wheel.