State press reported that about 70% of the unpaid wages are in the building industry, where armies of construction teams made up of surplus rural labour toil night and day in an ongoing urban building boom.

Following construction, the service industry, including restaurant and food businesses, were also behind in payments to migrant workers, the Xinhua news agency said, citing China's Communist Party-controlled trade unions.

The State Council, China's cabinet, issued a circular on the issue earlier this year, demanding that migrant workers be treated fairly and be paid on time, while local authorities in cities like Beijing have also issued new regulations demanding contractors pay workers, the China Daily reported on Monday.

"The problem of contractors who default on a worker's salary seems to have intensified recently," the daily said.

"Construction workers threatening to commit suicide to recover their earnings are common. As a disadvantaged group, they often resort to extreme means to get their money back."

According to China's Ministry of Labour and Social Security, there are some 207 million workers in China, of which 94 million are surplus rural labourers seeking work in cities.

Rural migrant workers, often known in China as the "floating population," have been the main force in channelling money to China's hugely impoverished rural areas.

Their income, however, has often come at great hardship, as they are not only widely discriminated against by city dwellers but they also often work in unsanitary and difficult conditions.