Climate-related disasters have displaced more than 42 million people in Asia over the past two years, the Asian Development Bank said Tuesday in a report calling for swift action to avert future crises.

"Asia and the Pacific is the global area most prone to natural disasters, both in terms of the absolute number of disasters and of populations affected," said the report launched in Bangkok, which was itself affected by flooding last year.

About 31.8 million people in the region were displaced by climate-related disasters and extreme weather in 2010 -- a particularly bad year -- including more than 10 million in Pakistan owing to massive flooding.

A further 10.7 million were forced to flee their homes last year, it said, warning that such events will become more frequent with climate change.

"While many of those displaced returned to their homes as conditions improved, others were less fortunate, struggling to build new lives elsewhere after incurring substantial personal losses," ADB vice president Bindu Lohani said in a foreword to the report, released at an Asian climate forum.

The bank says Asia has six of the 10 countries most vulnerable to climate change, with Bangladesh and India in the top two places on a list that also includes Nepal, the Philippines, Afghanistan and Myanmar.

"The environment is becoming a significant driver of migration in Asia and the Pacific as the population grows in vulnerable areas, such as low-lying coastal zones and eroding river banks," Lohani said in a separate statement.

"Governments should not wait to act. By taking steps now, they can reduce vulnerability, strengthen resiliency, and use migration as an adaptation tool rather than let it become an act of desperation."

The report, titled Addressing Climate Change and Migration in Asia and the Pacific, said governments in disaster-prone Asia-Pacific countries must enact a range of measures to stave off future crises.

Among other things, it recommended greater investment in urban infrastructure and basic services to accommodate the anticipated increase in migrant flows to the region's megacities.

"By taking actions today, governments can reduce the likelihood of future humanitarian crises and maximise the possibilities that people can remain in their communities or -- should deteriorating environmental conditions make that impractical -- that they have the real option to relocate to a more secure place with livelihood options," it said.

The ADB says the Asia-Pacific region needs to spend about $40 billion a year through 2050 to "climate proof" against the impact of global warming.