OSLO (REUTERS) - Nine Nobel prize winners in fields ranging from economics to medicine will try to come up with ideas this week to help fast-growing cities in Asia cope with global warming.

Organisers of the April 22-25 symposium in Hong Kong, where the laureates will meet, said cities were key to tackling climate change, with more than half the global population living in urban areas.

Within 30 years, 21 of a forecast 37 mega-cities of more than 10 million inhabitants worldwide will be in Asia, said the organisers, who include Germany's Potsdam Institute for Climate Impact Research.

Greener city designs, with energy efficient buildings and public transport, can help, they said in a statement.

"We have to do more ... This is an attempt to get focus on the issue," said Peter Doherty, an Australian medicine laureate, of the symposium, which has been held three times since 2007, in Germany, Sweden and Britain.