Japanese voters favour the deepest cuts in greenhouse gases under consideration by Prime Minister Taro Aso as part of a new UN climate pact, according to opinion poll results.

The survey indicated that 63 per cent of Japanese of voting age favoured a cut in greenhouse gas emissions of at least 25 per cent below 1990 levels by 2020 in a UN pact due to be agreed in Copenhagen in December, it said.

Mr Aso is due to decide during the middle of this month among six policy options, ranging from a rise of four per cent over 1990 levels, a goal favoured by Japanese industry, to a cut of 25 per cent.

"The world is watching Japan," Masako Konishi of the WWF environmental group told a news conference on the sidelines of 181-nation climate talks in Bonn, Germany. "The public do want strong targets."

The survey also said that 61 per cent of those asked reckoned that a strong 2020 goal would help the economy. The UN current Kyoto Protocol was named after the Japanese city where it was agreed in 1997.

WWF and other Japanese and international organisations - which all favour tough climate goals - commissioned the poll of 976 people by US-based Greenberg Quinlan Rosner from May 16 to 25.

Separately, a survey by the Potsdam Institute for Climate Impact Research showed that promises so far by all developed nations worked out as an overall cut of between 8.2 and 14.2 per cent below 1990 levels by 2020. Developing nations led by China and India want the rich to cut by at least 40 per cent below 1990 levels by 2020, the top end of a 25 to 40 per cent range outlined by the UN climate panel as necessary to avoid the worst of global warming.