Asia's cities are becoming increasingly vulnerable to natural disasters as they struggle with poor planning, population explosions and climate change, the Asian Development Bank warned on Tuesday.

Floods, earthquakes and other disasters claim tens of thousands of lives a year and cost billions of dollars in the region's cities and urban areas, but not nearly enough is being done to improve their defences, the bank said.

"The region has borne the brunt of the physical and economic damage of the sharp rise in natural disasters (globally) since the 1980s," the ADB said in a statement accompanying the release of a new study.

"Its people are four times more likely to be affected by natural disasters than in Africa, and 25 times more likely than in Europe or North America," it added.

Floods are the most common peril and have become three times more frequent across the Asia-Pacific in the past 30 years, the report said.

It found that the impact of storms on cities and urban areas has worsened due to chaotic urban planning and environmental degradation, as well as poorly-managed urbanisation and deforestation.

Meanwhile, millions of people are leaving safer rural areas for low-lying coastal cities, often driven to the economic hubs by poverty.

More than 152 million people in the Asia-Pacific are now vulnerable to natural disasters every year, up from 24 million in the 1980s, the study found.

Deaths from natural disasters across the region increased to more than 651,000 between 2000 and 2009, compared with fewer than 100,000 in the 1980s, it said.

Vinod Thomas, director-general for independent evaluation at the Philippines-based ADB, said governments in the region spent two thirds of disaster funds on restoring damaged infrastructure.

But only a third was spent on making these areas more disaster-proof.

"We have thought for too long that natural disasters come and go, that they are just an interruption to development, and that they can simply be dealt with after they strike," Thomas said.

"However, there is growing international recognition that the incidence and impact of natural disasters are increasing for a variety of reasons: persistent poverty, population growth, and climate change.

"Policymakers need to recognise that investments in disaster risk management are an essential means to sustain growth."