Police in Peru detained four male tourists, two Australians and two Canadians, for several hours after they were caught filming and taking nude photos at the country's famed Machu Picchu.

The culture ministry has put up signs at the Inca site warning people that taking their clothes off there was a "crime against culture" and would lead to immediate expulsion from the area.

The Australians, aged 22 and 24, used a camcorder and the Canadians, both 20, used an iPhone, police at a local police station said.

It comes after Peru vowed to step up surveillance at its famous historical sites to counter a growing trend of tourists taking nude photos and then posting them online.

It is not immediately clear if the four men acted together, separately or individually.

Machu Picchu, an Inca citadel from the 1400s, is a UNESCO World Heritage Site.

AFP