Police said the accident happened at 10:30 am at the Khao Tabtao or kilometre markers 59-60 on the main highway in Moo 4 village of Tambon Tha Kradan in Si Sawat district.
The curve was notorious for accidents and it is called the 100-bodies curve.
Police and rescuers rushed to the scene and found one body thrown out of the bus and seven more bodies inside. Rescuers took out the 28 injured people of the bus and rushed them to the Tha Kradan hospital. Police said 22 of the survivors were severely injured.
All of the injured were later forwarded to the Phahol Polphayuhasena Hospital.
The bus was chartered to take staffs of a firm in Samut Sakhon to join a seminar at a resort in Tambon Tha Tradan and the accident happened when the staffs were returning to Samut Sakhon, police said.