The cause of the crash on the Pan American Highway Tuesday night near the southern city of Ica is under investigation, Colonel Leandro Flores, chief of the highway police, told America TV.
"It was a head on type of collision," he said.
Among the dead were the two drivers and a Brazilian tourist on a bus traveling to Lima from the city of Cusco, police said.
Highway fatalities are common occurrences in Peru, many of them in accidents involving the country's many private bus companies.