A couple stands in front of a train of black horses in Southwest China's Chongqing municipality on their wedding day of March 7. [Photo/IC]

Men in Chinese mainland outnumbered women by 33.66 million in a country of more than 1.37 billion by the end of 2015. This imbalance has led to great concern over the difficulty of finding a partner for the left-over men, chinanews.com reported.

According to figures released by China's National Bureau of Statistics on Tuesday, the number of men in the Chinese mainland stands at 704,14 million while the number of their counterparts is 670,48 million by the end of 2015.

For every 113.51 boys born there were 100 girls (the natural rate is 102 to 107 boys to every 100 girls), the data showed.

Through still far beyond the natural rate, China's sex ratio at birth plunged by 2.37 from 115.88 of last year, the biggest drop in the last seven years.

The Chinese government strived to "lower the sex ratio at birth to 115 or below" during 2011-15, as it is proposed in the 12th Five Years Plan for National Population Development.

To balance the population, China further relaxed its more than three-decade-old family planning policy to allow all couples to have two children since the start of 2016.

China, like other countries with Asian cultures, held a historic preference for male offspring over female ones. Conservatives, especially old-fashioned clans in rural areas, regard boys as the only recognized heirs to carry on a family line.

The family planning policy, which was introduced in the 1980s to encourage each couple to have just one child, has pushed the sex ratio at birth up to some degree.

Some families prefer boys if they can only have one child, said Chen Jian, Vice President of China Society of Economic Reform, adding that the gap between sexes at birth will narrow as the two-child policy is implemented.