It is estimated that by 2020, China will have 24 million more men than women of marriageable age on the mainland.

"It is not only a population problem, but also a grave social problem as many men will fail to find a wife," Zhang said.

"Such a man may face an old age without the economic and emotional support of a wife and children," Zhai noted.

The provinces of Jiangxi, Hainan, and Guangdong now suffer the most skewed birth sex ratio, he said.

Authorities in Jiangxi province last year uncovered 2,064 cases of non-medical gender testing and sex-selective abortions.

They revoked the licenses of 312 medical workers and detained and sentenced 83 people.

"In places like Guangdong, despite its rising economic clout, people there still prefer boys to girls," Zhai said.

"That boy-preference norm will be reversed as people become more urbanized," he said.

In cities such as Beijing and Shanghai, the birth sex ratio is normal for residents who have a hukou, or residence permit, official statistics showed.

"However, it is imbalanced among migrant workers," Zhai pointed out.

He urged the government to target efforts particularly at rural areas and the migrant population in cities.

In addition to campaigns to end sex selection, the commission is also working closely on raising public awareness and implementing policies favoring families with a girl, particularly in the countryside, Zhang said.