World's largest lonely hearts club

The prospect of millions of men forced to go solo threatens major social and political problems for the tightly controlled and nation of 1.3 billion people, the most populous nation on the planet, experts told the conference.

China, like its neighbours Taiwan and South Korea, has paid the price for a rapid decline in fertility combined with a preference for male children, according to University of Texas researchers Dudley Poston and Karen Glover.

Since the 1980s, modern medical techniques which can determine the sex of a baby before birth, have led to high rates of abortion for female foetuses, according to the findings.

"From the year 2000 and continuing until 2020 there will be many extra boys of marriage age seeking females to marry, who will be unsuccessful in their courtship pursuits," the researchers said.

During China's baby boom of the 1960s the fertility rate peaked at 7.5 children per woman -- compared to 3.7 at the height of the US baby boom in the 1950s -- but plummetted following the introduction of the one-child policy in 1979, to 1.7 children per woman in 2001.

Despite the assertion by former Chinese leader Mao Zedong that "women hold up half the sky", the one-child policy led to massive sex selection in favour of boys from the 1980s.

As the ratio reached 120 male babies for every 100 female, the excess boys became known in Chinese as the guang guan or "bare branches".

According to the research, men who do not marry are more prone to crime than if they were married, raising fears of social and political instability.