The total number of migrants in China reached 230 million last year, or 17 percent of the country's total population, according to a report issued on August 6 by the National Population and Family Planning Commission.

With an average age of 28, 80 percent of migrants are from rural areas and nearly 45 percent of them were born after 1980, the annual report said.

The average monthly pay for those at or below the age of 35 was just 2,513 yuan ($395) in 2011. The figure represented a 29.4-percent increase from that of 2009, but was not nearly enough to cover their housing and health care in light of the increasing cost of living.

For migrants with a bachelor's degree or higher, the average monthly pay amounted to 4,608 yuan ($725).

Generally, only 51.3 percent of migrants hold fixed-term contracts, the report said, adding that they work an average of 54.6 hours per week, far above the 40-hour legal limit.