Two men and 16 water buffaloes were killed early on Thursday when a truck transporting 20 buffaloes lost control and overturned in Phayao's Muang district.
Police said the accident happened at 4.48am on the Ban San Khajao-Huay Nam Khao road in Moo 7 village in Tambon Tha Wang Thong.
The truck driver, Kitisak Phanphon, 30, and his passenger, Kamphol Srikham, 30, were killed. Fourteen of the animals were killed and the rest were injured.
Rescuers used iron cutters to free the men from inside the truck.
Police said the truck lost control at the curve of the road and overturned apparently because of the weight of the animals.