China has seen more than 300m people move into its cities since 1995 but the pace of migration of rural Chinese to cities, a dynamic hailed by Premier Li Keqiang as key to the nation’s development, is set to slow by a third in coming years, deepening economic-growth concerns.

A government report released this month projected a 6.3% rise in the share of people living in cities from 2013 to 2020, down from a 9.4% increase in the previous seven years.

Nomura Holdings Inc. estimates that slower urbanization will slice as much as 0.5% from annual GDP growth in China over the next decade.

The Chinese Premier, who has advocated an urbanisation-growth strategy for two decades, is up against a shrinking pool of rural workers, rising local-government debt and unhealthy air pollution in almost all big cities.

The urbanization blueprint, issued by the Communist Party and State Council on March 16, targets having 60% of the population in urban areas by 2020, up from 53.7% in 2013 and 44.3% in 2006.