The number of single men of marriageable age in China will reach at least 30 million in 30 years, the result of a widening gender ratio at birth in the last decades, experts said Monday.

Wang Guangzhou, a researcher at the Chinese Academy of Social Sciences, was quoted by the People's Daily as saying that the number of unmarried Chinese men between 35 and 59 will reach 15 million in 2020 and 30 million in 2050.

He said that poorly educated lower class men are far more likely to wind up single - males who only have a primary education or below accounting for 12.7 percent of the male population in 1990, but it increased to 15 percent in 2010.

Yuan Xin, a professor at Nankai University and expert on family planning policy, told the Global Times Monday that the number will likely exceed 30 million in 2050, as gender bias in favor of males at birth is still high in China.

The national average sex ratio at birth peaked at 121.2 males for every 100 females in China in 2004, while the standard ratio set by the UN is between 103 and 107 males for every 100 females, the People's Daily reported.

In 2015, the nationwide average was 113.5 males against 100 females, the seventh decrease since 2009.

Zhai Zhenwu, a sociologist at the Renmin University of China, said the continued imbalance was caused by the development of ultrasound technology in the 1980's, which aided the traditional family preferences for a son, the report said.

"The family planning policy which also promoted late birth had the negative effect on increasing the desire for people to select the sex of their child. Coupled with new, cheap and safe sex determination and selection technologies, this made the existing preference for a son become a reality," Yuan said.

China bans any testing for gender or selective abortion over gender preference.

Data released by the National Bureau of Statistics on January 20 shows that in the Chinese mainland, the male population reached more than 708 million at the end of 2016, while the number of females was more than 675 million.

China's sixth national population census in 2010 revealed that unmarried Chinese women above 30 years old accounted for 2.47 percent of the female population - almost two times higher than the figure reported in the 2,000 census, China Central Television reported in November 2016.

Yuan cautioned that recent trends of more well-educated Chinese women choosing to remain single will exacerbate the situation.

"Besides the marriage issue, a high single male population might also cause many other social problems such as sexual violence, women and child trafficking, not to mention the pension burden they will bring about when they get old," Yuan said.

The National Health and Family Planning Commissionsaid on February 6 that China would reduce its sex ratio at birth to 112 boys for every 100 girls by 2020.