Migrant workers at a construction site in Yichang, Central China's Hubei province, April 28. [Photo/IC]

China's migrant workforce reached 277.5 million in 2015, an annual rise of 1.3 percent, but the year-on-year growth rate has been decreasing since 2011, according to the National Bureau of Statistics.

A report released by the bureau on Thursday said the growth rate dropped 0.6 percent in 2015, and the percentage of workers younger than 40 years dropped 1.3 percent to 55.2 percent. The average age is 38.6, about four months older than in 2014.

The report defines "migrant worker" as a person whose household registration is in a rural area but who doesn't work in the agriculture industry, and those who work outside their hometown for more than six months annually.

The slower growth of the migrant-worker population might be a result of the slower growth of income. According to the report, the average monthly salary reached 3,072 yuan ($472), while the annual growth rate dropped 2.6 points to 7.6 percent. In the manufacturing sector, the growth rate dropped to 6.7 percent; the rate in the construction industry dropped to 4.4 percent.

In addition, 36.2 percent of migrant workers signed contracts with their employers last year, down from 38 percent in 2014, although the rate of signing short-term contracts－contracts for less than a year－grew by 0.3 percentage points.

One percent of migrant workers have unpaid wages owed them, 0.2 percent higher than last year. Unpaid migrant workers, on average had 9,788 yuan in wage arrears in 2015, with year-on-year growth of 2.9 percent.

Unlike State-owned corporations, small-scale construction companies usually don't sign contracts with workers, so the risk of wage arrears is greater, said Cui Hao, deputy director of the Overseas Engineering Company of China Tiesiju Civil Engineering Group Co.

"We have also noticed there are fewer young workers. Most of our workers are between 40 and 50 years old," he said. "It seems that the younger generation is less willing to do heavy physical labor, even though income in the construction industry is higher."

Wang Jiahui, a 40-year-old carpenter from Jiangxi province, said the contract he signed contains little about welfare, but lots of restrictions.

"I have friends who didn't get paid. They either left with empty hands or took out a lawsuit. But suing employers is a very difficult road," said Wang, adding that he has been working in Guangdong since 1997. "I hope my 15-year-old son can get a good education. I don't want my only son to become a migrant worker."

Contact the writers at pengyining@chinadaily.com.cn