The accident happened Tuesday morning when the driver lost control of the bus near kilometer 142 of the Los Libertadores highway, in the municipality of Puquio, 554 km south of the capital Lima, authorities said.
The police report said that the bus was heading for the city of Cusco, near the popular Inca ruins of Macchu Picchu.
Some of the passengers managed to jump off the bus before it fell, thus escaping injury. The injured were then saved by firefighters as well as by local residents who transferred them to the regional hospital of Ica.
The bus belonged to the Flores company, which manages bus routes between Lima and other major cities in Peru, including the tourism hotspot of Cusco.
An initial investigation into the cause of the crash, including interviews with the survivors, seemed to put the blame on the driver who was reportedly falling asleep at the wheel.