At least 48 people were killed when a bus tumbled down a cliff onto a rocky beach along a narrow stretch of highway, Peruvian police and fire officials say.

The bus was carrying 57 passengers to Peru's capital when it was struck by a tractor trailer and plunged down the slope, Claudia Espinoza with Peru's voluntary firefighter brigade said.

The bus fell about 80m and came to rest upside down on a strip of shore next to the Pacific, with the bodies of passengers strewn among the rocks.

"There is a large number of fatal victims," Col. Dino Escudero told RPP local radio.

Rescuers were working to pull victims from the hard-to-reach area in Pasamayo, about 70km north of Lima.

No road leads directly to the beach, complicating rescue efforts, Espinoza said, though police and firefighters managed to transport six survivors with serious injuries to nearby hospitals by helicopter.

He said the passengers included many returning to Lima after celebrating the New Year's holiday with family outside the city.

The narrow section of highway is frequently shrouded in mist and curves along a cliff that has seen numerous accidents.

Traffic accidents are common along Peru's roadways, with more than 2600 people killed in 2016.

A transport expert said while road conditions in the Andean nation had improved in recent years, lack of driver education and little enforcement of road rules still led to many fatalities each year.