The report defines middle-class people as those with assets of between $50,000 and $500,000, which puts Song squarely in this group, even if he is reluctant to be categorized that way.

That unwillingness to be put into a box may be understandable, particularly given that economists and other experts cannot even agree among themselves on what exactly the term middle class means.

A survey in the 2016 edition of The Blue Book of China's Society, a series of reports edited by sociologists with the Chinese Academy of Sciences, draws on three indicators: the occupations of a person and his or her spouse; total family income; and how much money they spend in a year.

The collective purchasing power of the middle class gives a strong fillip to consumption and the economy in general, the study says. That in turn helps prevent society becoming polarized, it says, adding that the social attitudes and values of the middle class are mostly positive, and can act as a role model.

Among the 3,017 people surveyed in Beijing, Shanghai and Guangzhou, 49.6 percent were middle class, and their average age was 40, it says. The survey put the average annual family income of the middle class in 2013 at about 197,900 yuan ($30,496) and their outgoings at 113,740 yuan.

They spent most on food and beverages, housing, apparel and accessories, entertainment and daily expenses. As well, they spent a sizable chunk of their income, an average of 10,000 yuan, on educating themselves and their child or children.

They spent a total of an hour a day getting to and from work, which is not that long, perhaps partly because 43.6 percent of them own cars. About 61 percent own their home; 30 percent work in private companies; 22 percent work in State-owned enterprises; 15 percent in public institutions; and 8.6 percent are traders.