If Han Jun is right, over the next three decades a population the combined size of Germany, France, Britain, Italy, South Korea, South Africa, Spain, Poland and Canada will up sticks and move to China's swelling cities. Mr Han, a rural expert at the Development Research Council, reckons that by 2040, the number of people in China's countryside will have shrunk by 500m to just 400m. On that assumption, China's city-dwellers would rise to well over 1bn, catapulting the urban population from 45 per cent of the total to around 70 per cent.

The startling numbers conjure up images of mass migrations and the trebling or quadrupling in size of big cities such as Beijing, Shanghai and Guangzhou. In practice, it is unlikely to be quite like that. China, after all, is a planned economy. Even so, McKinsey Global Institute, which has researched China's urbanisation trends, paints one scenario under which, by 2025, the country will have 15 super-cities with an average population of 25m people each. Meanwhile, many cities will “move” to the countryside as the state frantically constructs new urban centres in the interior and as changing land use blurs the distinction between village and town.

This is not futurism. By some counts, China already has some 170 cities with a population above 1m. That compares with nine in the US and two in the UK. In population terms, Tianjin is China's New York and Qingdao its Los Angeles.