GENEVA - Rapid urban growth combined with the effects of climate change will cause more and bigger disasters unless the world better prepares itself for them, senior U.N. officials said Tuesday.

People living in the slums of large cities where millions exist very close together and rescue services are poorly prepared, face particular risks, U.N. emergency relief coordinator John Holmes told reporters.

According to the U.N. International Strategy for Disaster Reduction, mega-cities such as Mexico City, Mexico, and New Delhi and Calcutta in India, are prone to severe earthquakes, while New York is at risk of dangerous flooding and tsunamis. Jakarta, Indonesia; Tokyo; Shanghai, China; Dhaka, Bangladesh; and Mumbai, India, are threatened by both quakes and floods.

With the number of people living in cities predicted to overtake those in rural areas this year according to the United Nations, Holmes said the potential for huge disasters was growing.

"You could have catastrophes of a scale you have not seen so far," he said.

Holmes said climate change, in particular sea-level rise, would inevitably increase the number and intensity of dangerous weather conditions threatening large cities.

"Climate change is already a reality and we're only going to _ in the best of circumstances _ be reducing its impact," he said, adding that "whatever carbon emissions reduction measures are taken now, we will still face virtually the same problems for the next 30, 40, 50 years."

Holmes urged governments attending an international disaster reduction conference in Geneva this week to act quickly to put in place measures that could save thousands of lives later.

He said experience had shown that taking simple measures to prepare and educate populations can be very effective, citing the example of Bangladesh.

The south Asian country regularly faces strong cyclones which in the past led to tens of thousands of deaths a year. But government measures to strengthen flood and storm protection mean that nowadays casualties are measured in the hundreds, Holmes said.

According to one of the largest relief organizations, the International Federation of Red Cross and Red Crescent Societies, investment in disaster risk reduction strategies has to be increased to US$1 billion (euro740 million) annually from US$400 million (euro295 million) at present, and targeted at community level.

"It's not the hazards that kill people, it's the way that society is organized," IFRC's disaster policy director Mukesh Kapila told The Associated Press.

He said every dollar (euro) spent on risk reduction would end up saving US$2-US$10 (euro1.5-euro7.40) in the event of a disaster.