Currently, there are about 18 million more males of marrying age than females, and a report has estimated that by 2020, males between the ages of 20 and 45 will outnumber their female counterparts by 30 million.
At the moment, 119 boys are born for every 100 girls in China, Jiang Chunyun, director of the China Family Planning Association, one of the country's largest non-governmental organizations, was cited as saying by the report.
The international average ratio is between 103 and 107 boys for every 100 girls.
Zhang Weiqing, head of the National Population and Family Planning Commission, said the gender imbalance has been evident since the 1980s, giving China the world's most serious gender discrepancy.
Zhai Zhenwu, the dean of School of Sociology and Population Studies at the Renmin University of China, told the China Daily: "If a gender imbalance occurs in one or two age groups, it can be adjusted. But when it stays and gets worse, the issue could become irreversible."
He blamed the imbalanced sex ratio on the traditional preference for male heirs, the availability of gender testing of fetuses with ultrasound and backward social security scheme in rural areas.
The sex discrepancy is highly visible in remote and poor areas, he said.
Zhai said the government was addressing the problem with education, subsidies and a strict regulation of ultrasounds and abortions. He also called for a more positive attitude toward women.