None were reported to have been seriously hurt.
Boonnha Kruetaiwong, 46, driver of the bus, which is operated by Samart Rodvijit Co, waited until police arrived at the scene.
He explained to them that he was taking the group from Phuket City to the Sea Sun Sand Resort & Spa in Patong, where they were staying.
As he was driving the bus up the hill, he shifted gears. The bus slid backwards, at which point he discovered that the brakes were not working.
The bus rolled backwards into the barrier at the side of the road, then tumbled over the barrier, landing on its side.
The injured were ferried to Patong Hospital for treatment.