From behind the closed doors of other homes in and around the town comes the sound of hacking and wheezing as the less fortunate struggle for breath. In others, there is only silence.

This is Wanshan, in Guizhou province, which was, until recently, the heart of China's centuries-old mercury mining industry. Since the government ordered the mines to close six years ago, however, it has become a high-altitude dormitory for the disabled and dying.

In this remote township, set amid dramatic mountain ravines and cut off from the buzz of metropolitan China by hundreds of kilometres of half-made roads, one of the most dangerous industries on Earth swallowed up generation after generation of workers.

Down dozens of pits and channels sunk deep into the hillsides of villages dotted around Wanshan, up to 14,000 men at a time dug for the 'liquid silver' that made their rural communities relatively prosperous - until a decade ago, when it was found that there was almost nothing left to dig for.

Centuries of mining had left the ground beneath the miners' homes hollow and perilously cavernous and the cost of drilling deeper to find new sources of mercury began to exceed the value of the metal they extracted.

From Beijing, thousands of kilometres away, the order came to halt mining and, at the stroke of a bureaucrat's pen, the livelihoods of thousands of families were cut off and youngsters expecting to follow their fathers and grandfathers into the industry found themselves without a future.

Years of hardship and recriminations have followed as men used to going underground to support their families find themselves trying instead to eke a living from the heavily contaminated soil surrounding their homes.

Some petitioned Beijing to reopen the mines or compensate the miners for their loss. Others left their families behind to seek out work in factories hundreds of miles away. Of those who stayed, some fell into crime and drug use as the local economy collapsed.

Now, in an apparent response to the poverty that the closure of the mines has brought about, the mercury industry has made a sinister return, with the opening of factories and enterprises that process imported mining waste into pure mercury in conditions that are arguably as perilous as those in the mines were.

In a village square overlooking two of the new mercury-processing plants, Yang Tongzai, 67, pants for breath as he chops up firewood with a small axe. A miner for 31 years, he spent his working life with mercury and knows its dangers well.

'We worked in mines up there,' he said, gesturing towards the arid hills behind him. 'Everyone did - it was the only work there was. We didn't question it. You could be a farmer or a miner but the soil here is no good - so we all went down the mines and of course we all got sick.

'I contracted lung disease in the 1980s and it got gradually worse and worse but I carried on working. What else could I do? Lots of miners got it, so it was fairly normal. I started coughing and I got a pain in my teeth. That's when I knew I was ill. But I didn't get the shakes like other people did so I suppose I was lucky.'

Lighting a home-rolled cigarette, he draws on it and shrugs when asked if smoking makes his lungs worse. 'How could it?' he asks. 'They are in such a bad condition it couldn't make any difference. It's been more than 10 years since I stopped working but my lungs are no better. I can only walk a short distance before I get out of breath.'

Yang supports his children and grandchildren on a miner's pension of 900 yuan (HK$1,022) a month. 'It's not easy of course but there's no work anymore. They have nothing to live on and I don't want them to work in the mercury factories. I don't want to see them end up like me.'

One of Yang's sons, a jobless young man with children of his own, stands listlessly by as his father struggles up a path of broken stones to the entrance of the lowest mercury mine and poses for pictures.

'I used to work down there a long time ago,' says Yang. 'Now no one will ever go down there again. They poured concrete down the shaft to stop people going too far into the old mines. There have been some terrible accidents around here.'

Desperation quickly followed the death of the mining industry. Locals would go on reckless solo missions down deserted mine shafts and use dynamite to try to blast rock containing mercury out of the stone. They would either come home with a few lumps to sell or die deep underground buried beneath rock falls in forgotten caverns.

Many of those who lost their jobs were consigned to a retirement of permanent disability, struggling to support their families on pensions of between 500 yuan and 900 yuan a month. Some lobby for more compensation for the infirmities they have suffered as a result of mercury poisoning.

One of them, Xie Guobin, is 48 but looks like a 70-year-old. With hands perpetually shaking because of his damaged nervous system, bleeding gums and loose teeth, Xie speaks in a rasping voice as he says, 'We've been going to Beijing to protest since 2002 but it doesn't do any good. I think we've been six times and we've also made many visits to the provincial government in Guiyang but it's all been to no avail.'

Another former miner, 52-year-old Yang Laoxin, says, 'I started working in the mercury mines in 1972 and I carried on until 2003, when they closed. It was hard and dangerous work but the money was reasonable. I used to work eight hours a day.

'I get 512 yuan in a monthly pension and it has to cover all my family expenses. I can't even afford to buy coal to keep us warm in the winter. Life is just too hard for us now there is no work. And my wife has to walk 1km to get relatively clean water from wells in the mountains. The water here has been totally contaminated by mercury.'

It is a gloomy recitation you hear from every ex-miner you speak to. 'I never thought the mercury would run out,' says Duan Huifa, 57. 'I had just turned 50 when I was forced to retire in 2002. Now I have to live on 590 yuan a month. My son can't find work. He's 17 years old and a drug addict. I hardly see him anymore.'

Families tell of former miners driven to crime, stealing corn and sweet potatoes from farmers, and of young women driven to work as prostitutes in neighbouring provinces to support relatives unable to make a living.

Tests have shown that the soil and water in the Wanshan region are contaminated with mercury. Villagers routinely draw their water from high mountain springs but, out of necessity, they grow vegetables in allotments next to their homes and some even directly outside the processing factories.

Government officials appear to be in a dilemma over what to do with the old mining communities. 'We've been told that the whole area is going to be turned into a tourist centre and we will be moved from our homes to a new village so this mountain area can be developed,' one shopkeeper says.

'Nothing has happened yet and we're not sure if they're telling us the truth or not. We don't know if we can trust them. Maybe they know something about the mercury poisoning or the ground erosion that we haven't been told. Maybe it just isn't safe for us to live here anymore - nobody is sure.'

Meanwhile, for a few, there is some money to be earned in the mercury-processing plants. At one facility less than a mile from some of the closed-up mine entrances, workers are drawn by wages four times higher than they could hope to get as farmers. Inside, they process mining waste from Russia, boiling it in huge vats to extract the ore, which is then sold on to middlemen in Beijing and elsewhere for use in industrial production.

They have only face masks to protect them from the poisonous fumes given off by the processing. About 50 people work here, one of the few plants that opened before the mines shut down.

'Between 70 and 80 per cent of workers fall sick after working here for a few years,' says 57-year-old Li Jian, a guard at the factory. 'Some of them get sick after working here for three years and some last as long as eight years but almost everyone gets sick in the end.

'They get mercury particles inside their lungs from the processing and then they get lung disease. You see people who start to get the shakes and then their teeth go rotten and fall out one after the other. Eventually they are too sick to work any more and they have to leave. They get a sickness allowance and a pension but they are like living ghosts. They are so damaged they can never work again.'

Pointing up the hill to the old mining village of Zhangjiawan, on the outskirts of Wanshan, Li says, 'You can see them in the village and they're easy to spot. They shuffle around and they have lost their teeth. You can see how sick they are.

'It's better now than it used to be. A few years ago, the workers had no masks and they would fall sick within six months. Now they last longer but the methods are still quite primitive.'

Speaking outside the factory gates, Mr Hu, a 37-year-old migrant worker from neighbouring Hunan province, says, 'The work is dangerous but the money is good, which is why we come here. I have a wife and child to support. Here, I can earn between 1,000 and 2,000 yuan a month. If I stayed at home and worked as a farmer, I would struggle to make 3,000 yuan in a whole year.

'I've been here for three years and I have seen many colleagues get sick. Sometimes they get very bad rashes on their face and you know then that the poisoning has begun and they may not last much longer. When they leave, we never see them again. I suppose they just go back home to die or to live off the money they've made while they were here.'

Officials at the factory refuse to let us in to see the conditions. 'You would have to write a letter to the local authorities to get permission,' the factory manager, who gives his name as Mr Tian, tells us. 'I'm afraid I'm simply not allowed to let people in, even to look.'

On the hillside overlooking the processing plant, Yang Tongzai breathes heavily as he carries the small pile of firewood he has chopped to his home.

'Some days I feel better than others and this is one of my good days,' he says with a toothy grin. 'I can't feel sorry for myself. I know I'm lucky to still be around.'