All passengers were Russian tourists.
The injured were treated at Sai Yok and Phaholpolpayuhasena hospitals.
Some were in critical condition.
Bus driver Kasian Karnket, 53, who is in police custody, said he had picked up the tourists from Pattaya at about 4am to take them to the Mahawangchang Elephant Camp in Kanchanaburi.
“The destination was just about 2 kilometres away when suddenly I lost control of the vehicle,” Kasian said.