More than 150,000 mainlanders obtained overseas citizenship last year, making China the world's biggest source of immigrants, a report released this week says. Many were wealthy and highly educated and had left in search of a more democratic society, a cleaner environment and better education opportunities, said the International Migration Report (2012) jointly released on Monday by the Centre for China and Globalisation (CCG) and Beijing Institute of Technology's law school. More than 87,000 mainlanders emigrated to the US last year, around 30,000 to Canada and the same number to Australia and more than 6,000 to New Zealand, it said. "The rich and educated elites are becoming the main force in the latest round of emigration," the report said. "The percentage of the middle-class in the total emigration group is rising." The CCG said the report was the mainland's first on international migration. Just over 6,000 mainlanders became permanent citizens of the US, Canada or Australia through investment last year, the report said. More than half of the Chinese emigrants to Australia were skilled workers, more than 40 per cent of skilled immigrants in the country. The exodus was closely linked to "issues including political reform, industrial structure upgrading, pollution and education", the report said. Liu Erduo , deputy director of Renmin University's school of labour and human resources, said the findings were a reflection of the unsatisfactory investment and employment environment on the mainland. "In one way, it shows more frequent talent migration as China becomes more open to the rest of the world," Liu said. "In another, it implies a gap in terms of payment and benefits offered to social elites between China and developed countries." Li Xiaogang, director of the Shanghai Academy of Social Sciences' Research Centre for Foreign Investment, said the upper crust was emigrating for a better environment - in terms of politics, pollution or justice. "Although China has developed so much economically in the past three decades, the social and political environment has remained unchanged," he said, "Many people actually achieved success in this environment and now they think this environment does not suit them any more." Another report, jointly released by the consultancy firm Bain & Company and China Merchants Bank last year, said more than 80 per cent of mainlanders who wanted to emigrate were most directly driven by better education opportunities for their children. While the brain drain boosted academic co-operation between China and other countries, it could also affect China's economy and cultural development, this week's report said. But Li said that the influence would not be profound, given China's large talent pool. The report said global migration increased from 195 million in 2005 to 214 million in 2010.