Census figures showed there were 271,500 construction workers in Hong Kong as of December last year. But 33,900 of the workers who completed the census said they did not have a job in the previous week.

While the census did not contain underemployment figures, unions said most construction workers were underemployed.

Unionists and workers believed less infrastructure construction, a sluggish property market and fewer public housing projects were among the reasons for their woes. Some pointed the finger at an agreement the government signed with the World Trade Organisation which required Hong Kong to buy pre-made blocks from the mainland, leaving less work for local builders.

The problems, combined with exploitation by employers, have seen hundreds of desperate metal workers stage daily protests on the streets this week, demanding better pay and shorter working hours.

Welder Tse Shek-king, 54, has not joined the protests, but watches his counterparts on television.

'I'm heartbroken when I see the workers. I feel it will one day be my turn. We're all being exploited and often not paid for months,' said the father of three.

From time to time, joblessness drove him to despair. 'Sometimes I can't sleep and drink beer to numb myself. Sometimes I cry in secret,' Mr Tse said.

The builder tried to hide his problem from his wife. For a decade, each day at 7am he would pack his bag and leave his Ma On Shan government flat to go to work - even on the days he had no job to go to.

'I didn't want my wife to feel worried that I didn't have a job. I just wandered around or went to the union to try to get help,' Mr Tse said. 'Other times I would go to the Labour Department to scan the computer for work.'

He tried to find other employment, as a transport worker or shop assistant, but had no luck. He said people thought he was 'old'.

To support his family and show his wife he had an income, he borrowed from his credit card account and racked up a debt of HK$200,000.

'Recently, my wife found out about it and wept for days,' he said.

Mr Tse is a foot soldier in an army of builders facing decline in what is known as a 'sunset industry'. Following factory workers who lost their jobs as firms moved to the mainland, they are the second group of workers to be sacrificed in the attempt to keep costs down.

In the heyday of the 1970s, Mr Tse had work year-round. He never worried about having to find a job, and enjoyed the boom years of 1995 and 1996 when Hong Kong built the airport and Tsing Ma Bridge.

He earned almost HK$19,000 a month during the good times. 'When we worked to 9pm, we were paid two days of money,' he said.

But all this changed in 1998 when Hong Kong was hit by the fallout from the Asian financial crisis, which dragged down sales and private construction. Figures from the Buildings Department showed the number of flats sold had dropped dramatically in recent years. In 2002, almost 40,000 units were built, compared to just 16,579 last year.

Chinese University economist So Wai-man said a reduction in major infrastructure building and public housing projects was another blow.

In 2002-03, the government started to halt the building and selling of government-subsidised housing to help correct the property slump. The number of newly built public housing flats dropped by half from 32,795 in 1996-97 to 17,153 in 2005-06. 'Most of Hong Kong's construction works are government works. The impact is big,' Professor So said.

To reduce unemployment, former chief executive Tung Chee-hwa set aside about HK$29 billion for infrastructure, but only spent HK$22 billion.

Public concerns about the West Kowloon and Central-Wan Chai reclamation projects proved another barrier to builders picking up their tools, Professor So said.

In the past 10 years, only 12 major public infrastructure projects had been built, while just eight were under construction, according to the government's Architectural Services Department.

But Ng Koon-kwan, of the Construction Site Workers' General Union that's organising the ongoing workers' protests, said the trend of government and private developers using mainland pre-casting parts had also replaced local labour.

These construction parts were cheap and environmentally friendly as they did not create dust at construction sites.

Mr Ng blamed the government for creating the problem by signing the Government Procurement Agreement of the WTO in 1997 without public consultation. The agreement states that signatories cannot favour local workers in awarding contracts and cost must be the prime consideration.

'This opened the door to mainland pre-fabricated housing blocks. The government started all these problems. Now most of the projects use these kinds of raw materials,' said Mr Ng.

To make matters worse, Mr Ng said, unlike many other signatories, Hong Kong's agreement applied to any project worth HK$50 million or more, a figure he criticised for being too low.

Workers and unionists said once the government started this practice in 1997, the private sector followed suit and now almost all projects used mainland pre-made structures.

Seeing the blocks of pre-made buildings, with walls and toilets fully completed and ready for use, saddened Mr Tse.

'A project which once needed 200 work days now just needs several days of work,' he said. 'Construction workers are only required for putting together those pre-made structures.'

The lack of jobs forced as many as 800 welders out of the industry, and only about 200 remained, Mr Tse said, who now earns about HK$400 a day.

To help the workers, the union urged the government to withdraw from the procurement agreement. It said the government should follow the example set by many of the 30 signatories and establish policies to ensure a certain amount of work would go to locals.

But Professor So disagreed. He said 'protectionism' could only work in big countries with massive markets and bargaining power. Introducing such measures in Hong Kong could reduce the city's competitiveness. While sad that workers were losing their jobs, Professor So said this was a natural social development.

Taking advantage of cheaper costs to increase competition was natural in a free market, he said,

and this was where Hong Kong's strength lay.

But Poon Man-hong, of the Confederation of Trade Unions, who had studied the impact of globalisation, believed this 'free market justifies everything' approach was too extreme.

'There should be a balance between free market and employment. Why do we just focus on one thing?' Mr Poon said.

Unionist Mr Ng agreed, adding the problem had hurt many families. 'Society should not just look at profits and free market and not see the social impact on people,' he said.

Being unable to find work had a devastating effect on many people in the industry, according to one worker in his 30s.

'Some are so depressed staying at home and have mental problems. They feel useless and some take drugs to numb themselves,' said the builder, who did not want to be named. He said two of his friends had resorted to crime. 'They had no money and no choice,' he said.

At 64, window fitter Shek Lam-sang knows that sense of desperation intimately. Every day he sits in his Sha Tin home, hoping the phone will ring with an offer of work. 'For two years I just get three to four days of work each month,' he said.

Earning less than HK$2,000 a month, Mr Shek relies on handouts from his adult daughter and other relatives to get by.

With many workers in their 50s and 60s, and lowly educated, economists and unionists have warned that retraining workers such as Mr Shek is difficult.

To compound their problems, Mr Shek said many workers were being exploited by their employers who required them to work longer hours without pay or refused to pay them for months. Workers dared not complain as they would be blacklisted by employers, he said.

Three decades ago Mr Shek, who grew up in a squatter camp, chose this line of work because it paid better than factory jobs. He never thought he would end up in this dismal situation, he said.

'What can I do? I have just primary two education. I am old and can't even work as a guard.'