Some 53 percent of the 5,000 migrant construction workers polled by the China Academy of Social Sciences and Tsinghua University said they did not have a legally mandated labour contract, according to the state-run China Daily newspaper.

Even among those that had signed labour contracts, as all are supposed to by law, 41 percent said they were not given copies of the document and 17 percent said they did not understand its content.

According to the survey, labourers worked an average of 10 hours a day, 27 days a month, but only 31 percent of the workers said that they were regularly paid on time.

Despite the law mandating that workers receive medical and retirement benefits, only 13 percent of the migrant workers said they had retirement insurance and 31 percent had medical coverage, the report said.

Forty-four percent of the migrant workers also said they were "looked down on" by urban residents, while only 3.7 percent of the labourers said they spent their leisure time off the work site, it added.

China is undergoing an unprecedented urbanisation process with over 130 million rural farmers descending on cities looking for jobs.

More than 40 million of those migrants work in the construction industry, the paper said. The survey's results, if extrapolated, suggests millions are exploited.

The poll was taken in the cities of Tianjin, Shanghai, Lanzhou, Guangzhou and Chongqing.

The survey was published after a slavery scandal surfaced last month, shocking the nation with accounts of children and men being forced to work in brickyards with no pay and under disgusting conditions.

Labour rights activists and international critics often accuse Chinese authorities and business chiefs of turning a blind eye to labour exploitation in preference for quick profits.

Rules Against Graft Tightened
Another report adds: China's top judicial bodies have tightened rules against official corruption, clarifying the illegality of bribery linked to the stock market, gift-giving and gambling, state press said Monday.

The move will crack down on major new types of bribe-taking, including receiving stock shares as gifts, being invited to buy houses and cars at "ridiculously low prices" and receiving bribes through gambling, the Xinhua news agency said.

The state supreme court and the supreme prosecutorial body jointly tightened the existing regulations on corruption, which were issued earlier this year, the report said.

The development comes ahead of several high profile corruption cases, including the expected trials of Shanghai's former top Communist Party official Chen Liangyu and former Beijing vice mayor Liu Zhihua.