The migrant worker population as well as their monthly income continued to grow in 2013, while many are still working overtime and more and more accruing unpaid wages, the National Bureau of Statistics reported on Monday.

The number of migrant workers increased last year by 2.4 percent year-on-year to 269 million, the bureau released in a report on Monday.

Better work opportunities in the eastern and coastal regions attracted the majority of the migrant workforce in 2013, the bureau said.

Last year's numbers showed the average monthly salary for migrant workers was around 2,609 yuan ($415), growing by 13.9 percent, and those working in traffic and for the postal service have the highest average income than workers in other industries, reaching 3,133 yuan.

However, they worked for around 10 months on average. In addition, the average workday was 8.8 hours, showing more of them worked overtime compared with data collected in 2012.

Besides, about 0.5 percent of migrant workers had had unpaid wages in 2012, but it rose to 0.8 percent in 2013, the first rebound after years of decline.