Chickens peck their way around satellite dishes that battle for space with pig pens and wood-fired stoves in the courtyard of Mr Jiang's earthen clanhouse, one of the most extraordinary buildings in China.

US intelligence once mistook the sturdy edifices, mostly built in a circle resembling a doughnut, for missile silos strategically hidden in the remote hills of southeastern Fujian province. Further research revealed that the “silos” were the ancient fortified homes of the Hakka, a fishing people who sought safety from persecution in this inaccessible corner of the country.

After centuries of quiet obscurity, the “tulou” — earthen buildings — have gained prominence since Unesco added 46 of the structures to its world heritage list this year. The Government fought for years to gain the listing and now tourists are pouring in.

Almost as quickly, the residents are moving out. With rising living standards, descendants of the clans that built the dwellings from a packed mix of sand, earth, mud and pebbles bound together with glutinous rice and brown sugar are building new brick-and-tile homes in nearby villages.

It is an exodus that disturbs Jiang Deqing, the chief of the Chengqilou tulou that once housed more than 100 people and now is home to only 32 — mostly elderly and young children. Mr Jiang said: “If anyone can afford to, then they move out. They want homes with lavatories and bigger rooms.”

Without inhabitants, the tulou deteriorate rapidly. Next door stands the Wuyunlou, its four-storey front wall cracked and buckling. Inside, wooden poles provide a flimsy buttress. A notice at the door forbids visitors from entering or climbing the steep stairs in case the structure crumbles. But three old people still live inside. Mr Jiang said: “The Government begs them to leave but this is their home and they want to stay.”

He hopes that the 600-year-old tulou, among the oldest of the houses built between 1300 and the 1960s, will be among the first to benefit from restoration after the world heritage listing.

Xi Songying, 71, tells of his pride in his 376-year-old clan home. Only eight families remain in the ruins that once housed more than 300 people. “The Government wants us to sell, but we refuse. We have always lived here.”

The younger generation is far less sentimental. From Qing Lian's three-storey brick house she can look down on the circular tulou that was her home for decades. “It was so inconvenient and dirty. My daughters have built this house where we have a bathroom on every floor. Only people without money still live down there.”

This poses a dilemma for the Government, which is eager to preserve the buildings but lacks the resources to maintain them - there are 20,000 in Yongding county alone — and cannot force residents to stay. The risk is that the tulou will soon be nothing more than museums.

Even if the ancient tulou cannot all survive, the Chinese architect firm Urbanus may have found a way to preserve the style. It is building a tulou affordable housing project in the southern city of Guangzhou. The circular structure will house 245 apartments, a dormitory, small hotel, shops and even a gym. Urbanus believes that the distinctive shape provides an alternative to the ubiquitous urban blocks.

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