Bangkok - A Thai tour bus taking university students on a field trip overturned on a road ramp Friday, killing 22 people and injuring 27 others, police said.

The driver apparently lost control of the vehicle about 3 am when it was coming down a steep hill in Nadi district, Prachinburi province, 140 kilometres north-east of Bangkok, and it overturned after crashing into a road guard up a dirt ramp.

The driver died in the crash along with 18 male and three female students from Kaset Techno Khon Kaen University.

Prachinburi police chief Major General Sanchai Chaiamporn said authorities were investigating the cause of the accident.

The Chatulong Tour Company bus was taking the university students on a field trip to Chantaburi province in eastern Thailand. (dpa)