The injured were taken to a hospital in the Lima suburb of Chosica, Highway Police commander Manuel Lozada said, La Prensa Latina reported.
Some of the surviving passengers aided first responders in pulling people from the wreckage of the bus, which ended up near the bank of the Rimac River.
The vehicle slammed into a rockface and plunged some 100 m (328 ft) to the bottom of a ravine.
Operated by Leon Express, the bus was en route to Lima from Huanuco, a city of around 200,000 people that is the capital of the region of the same name in central Peru.
Police suspect that the pre-dawn accident was the result of excessive speed or of the driver’s falling asleep.
Authorities closed a section of the highway, which links the Amazonian northeast with Lima.
Accidents involving intercity buses are all too frequent in Peru due to a combination of poorly maintained roads and the exhaustion of drivers who exceed the regulations for a number of consecutive hours behind the wheel.
HJ/PR
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