"In Asia, with half of the world's city dwellers, more than 1.5 million people die every year from diseases related to air pollution," the WHO Western Pacific office said in a statement from its Manila headquarters.

"About half a million deaths each year can be attributed to particulate matter and sulphur dioxide in outdoor air," the WHO said.

This is one of the potential problems faced by city dwellers as the size of the populations of cities increases rapidly, outpacing the growth in economies, services and infrastructure, the WHO warned.

"This will result not only in outbreaks of disease, but also an upsurge in crime, violence, environmental degradation, pollution, poverty and unhealthy lifestyles," the WHO added.

The urban poor will be especially vulnerable as they are more likely to lack adequate housing, sanitation and other basic services.

TERRA.WIRE