Mont Saint-Michel, an islet on France's northern coast, topped by an 8th-century Benedictine abbey, was France's first heritage site and among the first ever designated.[Photo/ Agencies]

A number of UNESCO's World Heritage Sites face major challenges, including the following:

Machu Picchu, Peru

This magnificent "lost city of the Incas" is cited by UNESCO as beset by logging, poor waste management and agricultural incursion but hasn't been placed on its list of sites in danger. Peruvian experts are raising other alarm bells, from vehicle fumes to the unceasing tread of footsteps producing a similar effect as a small-scale earthquake that could lead to the collapse of the temples and other structures.

The number of visitors－nearly 2,500 daily－appears to be overwhelming the site's safe carrying capacity. The 15th-century royal retreat was built high up in the Peruvian Andes to accommodate a population estimated at no more than 800.

Omori, Japan

This sleepy western Japanese town had "no outstanding universal value", according to the International Council on Monuments and Sites, which makes recommendations on world heritage sites. Its only attraction was a long-defunct silver mine and no tourist infrastructure existed aside from one eight-room guesthouse. But following intense lobbying by the Japanese authorities, Omori was inscribed in 2007. A year later, almost 1 million tourists poured in, rupturing the quiet lifestyle of the unprepared community.

Another controversial site in Japan was added to UNESCO's roster last year: factories and mines of the country's Meiji Industrial Revolution. Tens of thousands of Koreans, Chinese and Allied prisoners of war were forced to work at some of the locations, prompting the Chinese media to charge the listing "helped Japan cover up or glorify some of its past wartime atrocities". South Korea demanded that Japan make it clear that South Korean slave labor was used.

Lijiang, China

Amid widespread publicity, the 800-year-old town in China's southwestern province of Yunnan was declared a site in 1997, and is today one of the country's top domestic tourist destinations. Outsiders with more capital and skills moved in, sparking tensions with local residents who felt they were "losing their town". Already in the early 2000s, many streets of the old quarter were up to 90 percent in the hands of newcomers profiting by the mass influx.

Annual visitors swelled from some 150,000 before the heritage designation to 2.8 million three years later and some 16 million last year. Local culture has been adulterated in a complete tourism-oriented makeover. The charming houses are reproductions: Virtually the entire old town was razed by a 1996 earthquake.

Mont Saint-Michel, France

This offshore islet topped by a stunning 8th-century Benedictine abbey was France's first heritage site and among the first ever designated. Already a major pilgrimage destination in the Middle Ages, it underwent many transformations but has always drawn romantics and the faithful, even when it served as a prison during the French Revolution.

With a resident population of about 50 and only 100 hectares in size, it now attracts up to 2.8 million visitors a year. The Smithsonian Magazine wrote that its narrow, medieval streets are packed with tourists "who shoulder to shoulder, four to five thick, mill about like subway commuters at rush hour along the main street, which is nonstop cafes, hotels, restaurants and shops, selling every kind of souvenir imaginable".