The survival of the most important cave paintings in the world is in doubt because of a severe fungal infection that spread after an air-circulation system was installed to protect them, archaeologists say.

The 17,000-year-old paintings known as “the Sistine Chapel of pre-history” - the Lascaux cave in the Dordogne region of southwest France - are being damaged by black spots that are spreading at an alarming rate. Fragments of the cave walls have broken off and some colour tones are fading. Now Unesco is sending a delegation of specialists to the cave to determine whether it should be placed on its World Heritage in Danger list.

The paintings were discovered in 1940 by four teenagers who followed their dog into a large hole that had opened under the roots of a fallen pine tree. The extraordinary images of bulls, deer and horses have survived since the last Ice Age but are now being damaged by a bacterial and fungal infection. The deterioration is blamed on what the archaeologists describe as an “ill-conceived and disastrous” air-circulation system that was installed seven years ago.

Paul Bahn, Britain’s foremost specialist in Ice Age art, said that water could be seen running down the paintings, while black spots - some as large as a hand - were spreading across the walls and some of the paintings. He said that the cave had no means of circulating its natural currents of air and that, as biologists had yet to identify the exact nature of the spots, they had been unable to prescribe a proper treatment.

Lascaux contains a large entrance chamber and two main “galleries” - the Great Hall of the Bulls and the Painted Gallery - with about 1,500 engravings and 600 drawings in yellow, red and black mineral pigments.

Dr Bahn has called on the French Government to take action to save them. “The scandal of Lascaux cave is growing every day,” he said.

About 660 locations worldwide are designated as Unesco World Heritage Sites. Governments recognise an obligation, under the 1972 World Heritage Convention, to care for their heritage. Only 30 of the sites are considered at risk. It usually takes something as dramatic as a war, earthquake or other natural disaster for a site to be added, as in the case of the Buddhas of the Bamiyan Valley in Afghanistan.

In his letter to Francesco BandarÍn, the director of Unesco, Dr Bahn wrote of his “profound dismay and anxiety concerning the state of the cave”. He condemned the “fateful decision” to renew and update the cave’s electrical installations, writing: “The results of this bungled work have been catastrophic for the wellbeing and stability of the cave and its art. And despite the constant reassurances from the French Establishment, it is well known among specialists - who are receiving information from better informed or more objective sources - that the situation in the cave remains appallingly bad, and indeed is getting worse.”

He added: “If Lascaux is allowed to deteriorate further, and eventually to die, it will be an unforgivable blunder by the French authorities and an indelible stain on France’s international reputation.”

The paintings, which date from the Upper Palaeolithic period, redefined what was known about our creative development as human beings and our ability to construct images from abstract thought.

Laurence Léauté Beasley, of the International Committee for the Preservation of Lascaux, said that a critical point had been reached. Accusing French officials of closing ranks, she said: “According to their statements the cave is now recovering and the crisis is over. This could not be farther from the truth. Lascaux and its paintings are suffering from the ineptitude and lack of response of those charged with the care of the cave. It is suffering from a maze of bureaucracy. It’s like a plane without a pilot.”

The French Culture Ministry declined to comment.

Sites at risk

Afghanistan

The archaeological remains of the Bamiyan Valley, northwest of Kabul, are in a fragile state after the Taleban destroyed the two standing Buddha statues in 2001

Azerbaijan

The walled city of Baku sustained significant damage during the earthquake of 2000; Unesco has also cited poor conservation techniques

Egypt

Huge underground cavities have opened in the northwestern region of the town of Abu Mena. The risk of collapse is so high that the authorities were forced to fill the bases of some of the most endangered buildings with sand

Peru

The vast and fragile site of Chan Chan has fallen victim to natural erosion and plundering

Yemen

The historic town of Zabid, the capital from the 13th to the 15th centuries, is in decline and in a very poor state of conservation

England

Unesco is to consider placing Stonehenge on its endangered list when the World Heritage Committee meets in July, because of concerns about effects of traffic congestion near the site

Source: Unesco

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