La Oroya regional prosecutor, Hermelinda Zavala, told the Radioprogramas station that the bus apparently ran off the highway as it was speeding.
The accident happened about 100 miles east of the capital, Lima. She said the dead included a two-year-old girl and two teenagers. The bus driver has been detained. The country suffered its worst accident in 30 years in December when 51 people died in a bus crash near Cusco.