Many see them as the backbone of China's development.

From building city skylines to keeping streets clean, migrant workers have provided the crucial labor needed to power the country's rapid urbanization and economic growth.

There are reportedly about 200 million of such migrants who have traveled from rural areas to work in cities, with their numbers expected to continue rising.

To help accommodate the workers, four of the country's economic powerhouses - Beijing, Shanghai, Shenzhen and Chongqing - have been rolling out a slew of measures to improve lives in areas ranging from housing and education, to medical services and counseling.

Beijing

The capital has more than 5.1 million migrant workers in the construction and service industries, statistics indicate.

To help protect the workers, the Beijing bureau of labor and social security has stipulated that employers must cover workplace injury and provide medical insurance for their laborers.

To prevent overdue wages for migrant workers, employers are also required to submit salary payment documents to the authorities.

Similarly, the bureau has set up a 24-hour hotline, "12333", to provide answers related to policy, workers' rights and other labor issues.

The city also conducts professional training for migrant workers, partly funded by the government and employers, to help upgrade their skills and ensure that they remain employable.