MANILA, Sept. 25 (Xinhua) -- The number of urban inhabitants in developing Asia increased by five times from 375 million in 1970 to 1.84 billion in 2017, according to a report released by the Asian Development Bank (ADB) Wednesday

By 2050, the report -- the Asian Development Outlook (ADO) 2019 Update says it is expected to reach about 3 billion people, or around 64 percent of the region's population.

Cities are also growing geographically, often beyond pre-defined administrative boundaries, and connecting with surrounding areas to form city clusters, the report further says.

Using nighttime satellite imagery and grid population data that can assess where people actually live and work, ADB estimates that developing Asia in 2016 had 1,459 so-called "natural cities."

To remain engines of economic growth and jobs, the report says developing Asia's burgeoning cities need efficient transport networks and affordable housing backed by effective and coordinated land and economic planning.

"Asia's cities have been important contributors to economic growth, job creation, and innovation, but this isn't a foregone conclusion for future decades," said ADB Chief Economist Yasuyuki Sawada.

"Addressing weak infrastructure, congestion, housing, and education and health care services are critical if cities - and their host countries - are to remain dynamic," he said.

Sawada further said cities must function well as labor markets if they are to enjoy the economic benefits of agglomeration.

Established in 1966, the Manila-based ADB is composed of 68 members, 49 of which are from the Asia and Pacific region.