Charity foundation workers were treating the wounded and ferrying those more severely hurt to hospital.
The bus, according to police, was making its way up Patong Hill from the Kathu-Phuket City side at 7.13pm.
The bus lost power on the steep slope between the shooting gallery and the Patong City sign and slipped backwards down the hill, out of control.
It is believed the passengers were tourists from China.Most of the injured were suffering cuts from broken windows.
Early reports said there was a problem with the fuel supply to the engine of the bus.
The Thai driver and a guide were among the 15 people ferried to hospitals.