Ten people from the 24-seat bus, which set out from Phuket, were taken to hospital.
Five were admitted to Phang Nga Hospital while five who were more seriously injured were transferred to Vachira Phuket Hospital in Phuket City.
Three others on the bus were treated and allowed to leave.
The An Xin Tour bus failed to take the Phu Nga curve, which comes just before the right-hand turn to the pier for Panyee island off the main road between Phuket and Phang Nga Town.
Driver Sanya Anantapeach, 36, told police it was raining and he lost control of the vehicle on the curve.
The bus was carrying 10 Chinese tourists, a Chinese guide, a Thai guide and the bus driver.
It was bound for the Bor Saen Villa and Spa at Thap Put district in Phang Nga.
Reasons for the crash are likely to be closely examined by officials from the new Chinese Government consul-general office that recently opened on Phuket to improve tourism safety.