BEIJING - The two Chinese provinces of Shandong and Hebei on Friday relaxed their family planning policy to allow couples to have a second baby if either parent is an only child.

Twenty-seven of the 31 provinces, municipalities and autonomous regions on the Chinese mainland have now relaxed the birth policy. On Thursday, Henan, the most populous province, also adopted the policy shift.

"The shift will raise the birth rate, but the rate will still be at low levels," said Liu Qi, head of the Shandong provincial health and family planning commission. "In the long term, it is expected to have a limited impact on the demographic trend."

Most families in the countryside have had a second child, while in the cities, many couples show unwillingness to do so, said an official with the Shandong Family Planning Association.

Under the new policy, Hebei is expected to see an additional 65,000 newborns each year in the next three to five years, and the number will fall to 40,000 thereafter, according to the Hebei provincial health and family planning commission.

China's family planning policy, put in place in the late 1970s, was designed to curb population growth.

China announced an easing of the policy at the third plenary session of the 18th Central Committee of the Communist Party of China in November. The legislatures have started to review the regulation amendment this year.

The relaxation came as the country is coping with a declining labor force and an aging population.

The policy easing answered residents' expectations and will help promote balanced population growth, said Wu Xiangdong, deputy director of the Shandong provincial health and family planning commission.

Under the one-child policy, many couples, particularly in the countryside, had abortions as they prefer boys to girls. This led to a wide gender gap of 118 male births versus 100 female births in 2010.