Largely rural Henan, in central China, is source of many of the country's army of migrant workers who have helped transform the nation into the world's third-largest economy.

Henan's population jumped from 40 million in the 1950s to about 90 million in the 1990s, and while it would soon hit 100 million the rise had slowed notably over the past two decades, the China News Service said.

Henan could have been even more crowded without the central government's one-child policy, introduced three decades ago to curb population growth, the report added.

Without the policy, Henan's population would have an estimated additional 33 million people, it said.

China's urban population will overtake its rural population for the first time by 2015, with the number of people living in towns and cities set to top 700 million, state media said earlier this month.

The world's most populous country is projected to have 1.39 billion citizens by 2015, up from 1.32 billion at the end of 2008.

The world's most populous sub-national entity is India's Uttar Pradesh state, with 166 million people.