On a summer day, 52-year-old Wang Zhaogang paused to catch his breath after a few steps. He was wrapped up against the elements, since even a common cold could be enough to kill him, and his labored breath emitted a deep wheezing sound.

He was so frail that his heartbeat was visible beneath skin stretched across his rib cage. Wang, from Hunan province in central China, had lost 33 pounds over the past year and now weighed only 88 pounds.

Still, he’d traveled alone five times this year from his hometown in Sangzhi, one of the 10 poorest counties in China, to the southern megacity of Shenzhen to campaign for the city’s government to recognize and help workers like him.

Filled with resentment, he glared up at the city’s skyscrapers, which he had helped build from 2004 onwards – at the cost of his health.

“We are treated like ants … not humans,” said Wang, gasping for air. “I sold my life to Shenzhen. If I had known the danger of pneumatic drilling, I would never have done the work, no matter how poor I am.”

Wang learned his days were numbered in May 2017, when he found he had terminal stage-three silicosis – lung disease – linked to his years of exposure to silica dust on the job. Rather than quietly accept his fate, he has been petitioning the Shenzhen government for compensation.

He is among more than 600 workers from Hunan alone seeking money for medical care and compensation – a reflection of the forgotten human cost of turning Shenzhen, in Guangdong province, from a sleepy fishing village into a city with a gross domestic product of $338 billion in 2017.

While Shenzhen celebrates 40 years since China’s national opening-up policy that gave rise to its success, the plight of workers who built its subway lines and skyscrapers underscores that labor protection remains a problem, a decade after China introduced a law in 2008 requiring employers to issue contracts – and thus proof of employment – to their staff.

Gu Fuxiang, a 51-year-old fellow former worker from Sangzhi with stage-two silicosis, said that Shenzhen could not have achieved success “without the contribution of a group of silicosis patients like us.”

“I paid with my life for contributing to Shenzhen’s achievement,” Gu said.

Gu’s older brother died from silicosis in 2016 at 51, and a younger brother with suspected stage-one silicosis is waiting for an official diagnosis.

“I need this money badly,” Gu said. “I need it to support my parents, for my children’s education and to pay off debts. I don’t have much time left. I need to make arrangements for my funeral.”

Silicosis is an incurable form of pneumoconiosis, a lung disease caused by prolonged inhalation of airborne silica dust.

Pneumatic drill operators drill holes deep into the hard granite beneath Shenzhen to prepare sites for building foundations. The Sangzhi workers said that when they were hired, such work earned a daily rate of 200 to 300 yuan ($29 to $44), three times higher than other types of construction work at that time.

Migrant workers, who number about 287 million across China, worked most of the drilling jobs. Since the 1990s, laborers from Hunan have flocked to cities including Shenzhen to pick up drilling work for quick cash. But in the 2000s many began falling ill and dying.

China’s most widespread occupational illness, pneumoconiosis, is commonly found among coal miners but is suffered in varying stages by an estimated six million-plus Chinese migrant workers, according to Love Save Pneumoconiosis, a Beijing-based charity dedicated to helping them.

Data from the Chinese public health ministry shows that pneumoconiosis accounted for 22,701 of the 26,756 new occupational illness cases it recorded in 2017. Silicosis alone killed 46,000 people around the world in 2013, according to a study by the Institute for Health Metrics and Evaluation in Seattle.

“A lot of them got ill with pneumoconiosis simply because they had been breathing in dust all day every day with no protection,” said Geoffrey Crothall, a spokesman for Hong Kong-based China Labour Bulletin, which promotes and defends workers’ rights in China.

Workers’ petitions have resulted only in small charitable handouts, partly because most workers lack documents proving they were employed at the sites where they worked before falling ill.

More than 200 workers made their sixth visit to Shenzhen to press their case to the city government in September, and planned another trip this month after officials failed to honor past promises to help.

Minutes from their meetings, provided by workers, indicate that the authorities had pledged to accelerate processing compensation claims from 227 workers who were able to produce confirmed employment records.

The notes stated that workers were also promised that mobile clinics would be sent to Hunan to examine other workers, that Shenzhen city leaders had agreed to visit ailing workers, and that those with no proof of employment at the sites had been offered discretionary handouts from the city government.

Gu said that more cases were being identified after Hunan health authorities launched a province-wide migrant worker health screening campaign last year. The rise may also relate to the latency period of silicosis, which can take years to produce symptoms.

Professor Pun Ngai, a China labor studies expert at the University of Hong Kong, said that some workers had not joined those petitioning in 2009 because they did not realize they were sick.

“But in the past two years, new cases just exploded,” Pun said.

The number of cases is only likely to increase, according to Wang Yuehua, 50, who is another stage-three silicosis patient leading the petition efforts.

“It’s now 2018, and the dangerous jobs still exist,” Wang said. “There is no improvement. Many of the workers continue to suffer from pneumoconiosis. [The government] keeps putting us off. We can do nothing.

“But we are determined. If the petition here is not working, we want to go to the Guangdong provincial government in Guangzhou. If Guangzhou doesn’t work, we may go to Beijing.”

Pun blamed poor enforcement of the 2008 labor-contract law by all parties for driving ailing workers who lack employment records to the long and winding road of petitioning for an official occupational illness diagnosis.

Research in 2016 by NGO Love Save Pneumoconiosis showed only 9.5% of migrant workers with pneumoconiosis had signed labor contracts with their employers. This means most would struggle to prove they might be eligible to claim compensation for a job-related illness.

Sangzhi worker Zhong Jiaquan, a 46-year-old stage-three silicosis patient, said that occupational health clinics in Shenzhen would not even examine workers without employment records, effectively cutting off hopes of moving their cases forward.

“We are sick and dying; the government should at least foot our medical bills,” he said, lighting a cigarette. Given that he faced a terminal disease the risks of smoking, he shrugged, were no longer a concern.

“They cannot just sit there and watch us die. There is nothing more sad than to watch your brothers die a slow and painful death, leaving behind young wives and children. Soon that will be us.”