The Chachapoyas once commanded a vast kingdom stretching across the Andes to the fringe of Peru's northern Amazon jungle until they were conquered by the Incas in the 15th century.

The Incan empire was itself overrun soon after by the Spanish and details of the Chachapoyas and their way of life were lost or destroyed in the widespread pillaging that followed.

Now a team of archaeologists, working on a tip-off from a local farmer, have uncovered a hugely significant burial site at the bottom of an 820-foot deep cave.

The researchers have so far found five mummies, two of which are intact with skin and hair, as well as ceramics, textiles and wall paintings, the expedition's leader and regional cultural director Herman Corbera told Reuters.

"This is a discovery of transcendental importance.

We have found these five mummies, but I believe there could be many more, " Corbera said. "We think this is the first time any kind of underground burial site this size has been found belonging to Chachapoyas or other cultures in the region, " he added.

The tribe's own name is unknown. The word Chachapoyas is thought to come from the Quechua for 'cloud people' . . . and is the name by which they were known to the Incas because of the cloud forests they inhabited in what is now northern Peru.

A white-skinned people who were famed as ferocious fighters, the Chachapoyas held out against the Incans, who had built an empire stretching from southern Chile to northern Ecuador, until their conquest by the Spanish in the 1530s.

Today, the 'cloud people' are best known for their stone citadel, Kuelap, with more than 400 buildings and massive exterior stone walls, that is often referred to as the Machu Picchu of the north.

Corbera said the walls in the limestone cave near the mummies were covered with wall paintings of faces and warrior-like figures that may have been drawn to ward off intruders and evil spirits.

"The remote site for this cemetery tells us that the Chachapoyas had enormous respect for their ancestors because they hid them away for protection, " Corbera said.

"Locals call the cave Iyacyecuj, or 'enchanted water' in Quechua, because of its spiritual importance and its underground rivers, " he added.

"The idea now is to turn this cave into a museum, but we've got a huge amount of research to do first and protecting the site is a big issue."