Migrant workers covered by employers' liability insurance also surged by 79.3 percent to 22.4 million in the first nine months of the year, thanks to China's stronger efforts to protect the rights of migrant workers.

China's economic boom has driven an unprecedented army of about200 million people to swap farms for factories, construction sites and mines as they seek a higher income.

A survey by the State Administration of Work Safety (SAWS) in nine provinces shows that migrant workers account for 80 percent of China's 30 million-plus construction workers. They also make up56 percent of the workers in mining and dangerous chemicals and fireworks factories.

The survey also shows that almost all the workers at small collieries are migrant workers. Even in state-owned collieries, almost all the non-management jobs are filled by migrant workers.

Poor safety facilities, slack safety rules and the lack of proper training have made migrant workers the most vulnerable group in terms of work safety.

To protect the interests of migrant workers, the Chinese government has been pushing for wider insurance coverage in vulnerable industries such as coal mining and construction.

By the end of last year, almost all the migrant workers in major state-owned collieries had been covered by employers' liability insurance.

China is also trying to strengthen the training of migrant workers, as the SAWS survey shows that 90 percent of industrial accidents are caused by human error, and 80 percent occur in work places dominated by migrant workers.

A SAWS guideline states migrant workers in dangerous industries must receive no less than 72 hours of safety training before they begin work. For those in the construction industry, the minimum requirement is 32 hours. The guidelines also require no less than 20 hours of safety training for each worker each year.