BEIJING — China now has more than 100 million people with no siblings since introducing rules in the late 1970s that limit many couples to only one child, a state news agency reported today.

China is the world's most populous country, with 1.3 billion people. The government says the one-child rule has prevented about 400 million births.

The 100 million-plus only children make up about 8 percent of China's population, Xinhua News Agency reported, citing information from a weekend forum hosted by the Shanghai Population Welfare Charity Fund.

The one-child policy was designed to control China's exploding population and ensure better education and health care. The law includes exceptions for ethnic groups, rural families and families where both parents are only children.

In 1982, Chinese households averaged 4.4 people. In 2005, the average was 3.1 people, the agency said.

Critics say the policy has also led to forced abortions and sterilizations as local authorities pursue birth quotas set by Beijing, plus a dangerously imbalanced sex ratio as families abort girls out of a traditional preference for male heirs.

Though commonly called a one-child policy, the rules offer a welter of exceptions and loopholes, some of them put into practice because of widespread opposition to the limits. For example, in large parts of rural China, most families are allowed a second child, especially if the first was a girl.