Authorities in Guangdong, one of China's most populous provinces, will stick to the family planning policy and promote free premarital and pregnancy checkups to curb high birth defect rates, a senior official said.

Zhang Feng, director of the provincial population and family planning commission, made the remarks over the weekend at a seminar marking World Population Day, which fell on Sunday.

Guangdong is home to more than 100 million people, including about 97 million permanent residents - the largest number in the country - at the end of last year. Up to 1.2 million more will be born by the end of this year, Zhang said.

Per capita farmland in the province measures less than 0.03 hectares - not even half the national average and far less than the United Nations' warning level of 0.053 hectares, he said.

Because the huge population is stifling economic and social development, Guangdong still needs to stick to the family planning policy in its 12th Five-Year Plan (2011-15), Zhang said.

He added that birth defects remain a problem because of endemic diseases, such as the blood disease thalassemia.

Up to 7 percent of newborns in Guangdong have mental or physical disabilities, which is more than the national average, he added.

A document promoting free premarital and pregnancy checkups across the province is expected this year. The checkups are being offered in several cities on a trial basis.

The population's sex ratio in Guangdong has gone from 130 men for every 100 women in 2000 - the second highest in the country at the time - to 112 men for every 100 women now, Zhang was quoted by Southern Metropolis Daily as saying. The national ratio last year was 119 men for every 100 women.

But Guangdong's sex ratio remains imbalanced compared to the UN's figure for a global average of between 103 and 107 men for every 100 women.

Huang Zhilian, a domestic worker in Guangzhou, said: "I believe it's a big issue. Men, especially disadvantaged ones, will have trouble finding wives."

Fetal sex determination and strong preferences for having boys are the main causes of the imbalances, Zhai Zhenwu, dean of Renmin University's school of sociology and population, was quoted as saying by People's Daily.

There will be 24 million more men than women of marriageable ages by 2020, according to a Chinese Academy of Social Sciences report issued last year.

Also, the 30 million migrant workers in Guangdong violate the family planning policy more often. The number of babies born to the mobile population of six of Guangdong's relatively wealthy cities exceeds that of local residents.

In addition, migrant workers, who spend long periods away from their spouses without fixed sex partners are also susceptible to high rates of sexually transmitted diseases, including HIV/AIDS, Zhang said.