The population control measure has prevented almost half a billion births since it was introduced in 1979, Chinese experts claim.

But it has turned into a demographic time bomb as the population ages, storing up huge economic and social problems for the country as well as fostering a gender imbalance.

"Over-population remains one of the major challenges to social and economic development," Li Bin, director of the State Population and Family Planning Commission told Xinhua, adding China's population will hit 1.45 billion in 2020.

"Maintaining and improving the existing family planning policy and keeping a low reproduction rate, along with addressing the issues of gender imbalance and an ageing population, will be the major tasks in the future," he said.

His remarks came as the world's population is expected to hit seven billion on Monday, according to the United Nations.

Critics blame the "one-child" policy for creating gender imbalances -- sex-specific abortions are common and female infanticide and the abandoning of baby girls have also been reported.

The policy also puts huge pressure on only children to support their parents and two sets of grandparents.

Guangdong in southern China asked Beijing in July for permission to partly relax the policy and allow couples where just one parent is an only child to have a second baby.

But Zhang Feng, director of the province's population and family planning commission, said there would be "no major adjustments to the family planning policy within five years."

Li of the family planning commission defended the policy, saying China's population would have hit 1.7 billion without the requirement.

The show at the Taipei Fine Arts Museum also showcases other controversial works by Ai, including a picture of Wei Jingsheng, one of China's best-known democracy activists, who spent 15 years in a Chinese jail before being exiled to the United States.

Ai, who is banned from leaving Beijing, suggested that his absence from the exhibition, his largest solo show ever in a Chinese community, had significance in itself.

"(My absence) will give the exhibition a special meaning," he said in a statement issued by the museum.

Ai, who is one of the most outspoken critics of Communist Party controls and censorship in China, is currently being investigated for tax evasion and has been ordered not to leave Beijing.

He was released in June from three months in detention, following outrage around the world over the way he was treated by the Chinese government.

The influential Art Review magazine recently named Ai the world's most powerful art figure, drawing criticism from Beijing.

The three-month "Ai Weiwei Absent" show opens on Saturday and features 21 sets of Ai's creations from 1983 to present, including installation pieces, photography, sculpture, and videos.

The centrepiece is "Forever Bicycles," a giant installation of 1,200 bicycles placed on top of each other, symbolic of a changing Chinese community, for which Ai finalised the design after his release.

A Taipei city government spokesman has said that Ai's wife Lu Qing is planning to come to Taipei to see the show next month.