A US-based long-standing Chinese critic of China’s family planning policies says Beijing has inflated the country’s official population total by as much as 100 million people and should abandon limits on births as soon as possible.

In two unpublished research papers, Yi Fuxian, a senior scientist with the department obstetrics and gynaecology at the University of Wisconsin-Madison’s medical school, said China’s actual population at the end of last year should have been about 1.28 billion, and not the 1.38 billion calculated by the National Bureau of Statistics.

By Yi’s estimates, China is already the world’s second-most populous country after India. But according to the United Nations’ 2017 “World Population Prospects” report, India will not overtake China in population until 2024.

The 100 million gap is an upward revision of the 90-million difference Yi suggested at an academic symposium in Beijing in May, causing a stir.

China may have 90 million fewer people than claimed (that’s twice of Spain’s population)

He said he changed the number to take account of Chinese migration to other countries.

Yi said local authorities tended to inflate population numbers to get more central government funding for education, health and transport.

Yi’s estimates have found little support in China.

Yang Yiyong, a researcher with the National Development and Reform Commission, said the estimate defied common sense, according to the official China Economic Weekly.

“China’s population data is much more accurate than its GDP [numbers],” Yang was quoted as saying.

Yi has long been a critic of China’s one-child policy and laid out his opposition in his influential book, Big Country with an Empty Nest.

The book was only allowed to be published in mainland China in 2013 when Beijing began to acknowledge the huge social costs of the one-child policy.

China sees 1.3 million more new babies in 2016 ... but workforce shrinks as population ages

China started to embrace a two-child policy in early 2016 and Yi was invited to speak at the Boao Forum for Asia that March, a sign that his views were tolerated by Beijing.

But Yi’s public doubts about China’s population figures have made him unwelcome again and his Chinese social media accounts have been blocked.

According to official data, China had 17.86 million new births last year, a very small rise from the 16.55 million the country reported in 2015.

China’s rapidly greying society and shrinking labour pool are seen as big hurdles for the country’s future economic development.