For every 100 baby girls born in 2005, there were 118.58 baby boys, and the gap will continue to widen, said the report by the State Population and Family Planning Commission.

In southern provinces such as Guangdong and Hainan, the picture is grimmer: There are 130 baby boys for every 100 baby girls.

Since 2005, the number of men reaching marriage age has been much more than women. "The increasing difficulties men face finding wives may lead to social instability," said the report by more than 300 Chinese demographers after two years' research.

This is because Chinese traditionally prefer boys, and with their financial status improved, those in the booming coastal areas can afford to find out the sex of the foetus.

The picture will be starker in the countryside than in cities, said the report.

To solve the problem, there must be a full-fledged social security system so that rural residents don't have to depend on their sons when they get old, said Wang Guangzhou, researcher at the Institute of Population and Labour Economics affiliated to the Chinese Academy of Social Sciences.

According to the report, China's population will increase by 200 million in 30 years, which means the total population will hit 1.36 billion by 2010 and 1.45 billion by 2020 before peaking at 1.5 billion in 2033.

The figures are calculated on the assumption that China's birth rate will be kept at the current 1.8 meaning one woman of childbearing age giving birth to 1.8 babies. The country must maintain the ratio if it wants to build itself into a well-off society reaching the goal of US$3,000 per capita of GDP in 30 years, said the report.

The silver lining is that "for a long time to come, China will not be short of manpower", it said. There were 860 million Chinese of working age between 15 and 64 in 2000, and the number will reach 1.01 billion in 2016, which is "more than the total number of working age people in all the developed countries".