Her T-shirted charges trailing behind her, the young guide swept into Huang Puxin's home and flicked her tour flag towards the centenarian, who was waiting on the sofa beneath a giant bas-relief inscribed with the word "longevity". "The old man is 113," she mumbled into her headset, turning away.

The tourists stuffed cash into piled-up red envelopes and moved in beside Huang, patting his knee as they handed him the money and posed for a picture.

Huang has lived through wars, famines, the rise and fall of Maoism and much more. But his life's latest turn may be its unlikeliest: reinvention as a tourist attraction. Bama county, in southern Guangxi, used to be one of China's poorest places. Now, thanks to residents such as Huang, it is a travel hotspot.

Famed for centuries for its residents' unusual longevity, it now has 81 centenarians. Proportional to population, that is roughly five times China's average.

A decade ago the best-known settlement in the county rebranded itself as Longevity Village, and in the past few years coverage and word of mouth have prompted a surge in visits. More than 640,000 people came in the first five months of 2013, boosting the economy by 406m yuan (£41m), say officials.

An estimated 20,000 health tourists – many times the number of native residents – live in the surrounding district, staying for months at a time. Thousands more arrive on coach trips, to receive the benediction of the oldest residents.

Longevity Village in Bama, Guangxi, has undergone rapid development in the past few years as tourists come to discover the secrets of long life. Photograph: Tania Branigan for the Guardian

Thick stands of bamboo, graceful eucalyptus and glossy chestnut trees line the road into Bama. Its stunning karst landscape is pierced by caverns and rises into steep crags.

"Even in winter it's not cold at all. The mountains are beautiful and the river is the colour of jade," said Dai Guifang, 65, who runs a construction firm in north-eastern China. "The air is very good. I feel uncomfortable if I smoke even half a cigarette in Shenyang – but in Bama I'm fine if I smoke a pack a day." Her late husband spent his last few months here. She believes the stay prolonged his life and reduced the pain of his stomach cancer. "A lot of people were sick but got better after living there – it's the water. It has a lot of minerals," she said.

Most tourists drink the waters and the bolder ones bathe in it, with mixed results. Some have drowned, report residents. Further up the valley, scores of middle-aged and elderly people perch on rocks in the gloom of the giant Baimo cavern. A few stand with their faces turned to giant boulders, pressing their hands to the stone. This is geomagnetic therapy, they say, enthusing about its beneficial effect on the heart, the brain and even varicose veins.

Cui Xuedong, 58, pulled up his shirt to show the scar across his torso; he had just had a second round of surgery for liver cancer. He was sceptical when a neighbour urged him to try Bama but said the impact was unmistakable: "After 30-odd days my face was rosy again. When I arrived I felt exhausted every afternoon, whatever I did in the morning. Soon I could swim a kilometre and still kick a shuttlecock around."

He has now moved to Bama and runs an organisation bringing city dwellers to the area, while his wife exports hundreds of tonnes of its water.

Cui believes the area's geomagnetism and negatively charged oxygen ions are as important as its relaxed, modest lifestyle. Experts scorn that and see simpler explanations for the town's longevity: in large part, poverty and isolation.

Yang Ze, deputy director of the Institute of Geriatrics at Beijing hospital, began researching Bama's secret in the mid-90s. One key, he said, is natural selection. The area is remote and mountainous. In the old days, it took three days to leave the hills, so there was relatively little mixing with the outside world. In tough conditions, without medical treatment, the strong genes remained; the weak were eliminated.

In particular, he said, Bama residents have mostly inherited a gene from both parents that helps the body to produce a protein called apolipoprotein-E. That combines with fats to form a lipoprotein that reduces excess cholesterol.

Lifestyle played a part, too. People worked hard in the fields. Much of their food was steamed, not fried. When Yang first arrived, they ate "rice porridge with a bit of salt, and hemp oil", and seldom consumed meat. Old people were surrounded by relatives. "They were not lonely and were happy. They were calm, had fewer desires, did not compete, and were more optimistic," Yang said.

Now the area's new-found popularity is destroying its very attractions. "The new residents bring a Beijing lifestyle to Bama. They shout in the mountains; they turn up the music to do exercise in the morning," he added.

Hammers and drills disturb the once-tranquil scene thanks to the soaring demand for rented property. Cars clog the narrow streets, pumping out fumes. Residents complain the river is polluted because visitors dump rubbish and because the sewage systems cannot cope with so many people. These days, the young prosper by selling goods to tourists rather than by labouring. And the eldest can sit at home, on a couch, and wait for red envelopes.

As the area has grown wealthier and less isolated, it has also grown less healthy. Bama is a microcosm of China: its burst of development made its shift from diseases of poverty to those of affluence even more pronounced.

A tourist stops to talk to Huang Meijian, 99, and her 76-year-old niece Huang Meijie. Photograph: Tania Branigan for the Guardian

"The centenarians eat braised pork every day. Since they have got richer, their diet has been changing," Yang said. "Last time I was there, I told them problems such as high blood sugar and high blood pressure were appearing in this village, and that if they were not careful, it would lead to death. They did not listen to me and despised [my advice]. They said they had just started to get rich, and we were trying to stop them."

In 2005 there were 17 or 18 people aged over 100, but these days there are just two, he thinks – not seven, as the village claims. An Italian, aged 111, is officially the world's oldest man.

Yang believes Bama could soon lose all its centenarians. Not only are the next generation likely to have shorter lives, even those who are already elderly are unlikely to reach 100, he suggests. But having struggled for years to feed themselves, Bama's elderly see little to lament in this new world of plenty. "In my time there were a lot of wars. A lot of people starved to death. A lot of people were hungry," ruminated Huang Puxin.

"I have had a lot of happy times, but the best is now," observed Huang Makan, a few houses down, with a flash of her exquisite smile.

A tiny figure in a padded jacket, with a jade bracelet on each wrist, she says that she is 108, has never had a day's sickness, and enjoys the constant company. "Many people come to see me. I hope I live until 200," she confided.

Additional research by Cecily Huang

How they did it



Living a long life, Bama-style, according to those who have managed it:

Huang Puxin, 113: Be a good person. Have a good heart.

Huang Makan, 108: Eat green, organic, simple foods. I eat sweetcorn congee a lot. I don't have many demands.

Huang Meijian, 99: Work and walk around every day.

Dr Yang Ze's (strinkingly similar) advice

1. Treat yourself and others well, be more tolerant to yourself and others, be optimistic. Love life, love your family, have love to offer to people and be open-minded.

2. Have a healthy lifestyle. Neither eat too much nor stay hungry. Keep your diet bland. Eat more vegetables and fruits, and less protein and carbohydrates.

3. Do more exercise. All centenarians help themselves and do everything by themselves … They go farming in the mountains, they cook for themselves.

4. Bama women have children late: they give birth to their first baby at 27 and the last baby is usually around 42 or 43.