Climate change has emerged as the most contentious issue at this year's summit of the G8 top industrialised nations, which began today in Japan.

European Commission President Jose Manuel Barroso said the G8 nations must reach agreement among themselves on climate change measures and avoid taking the approach that "I will do nothing unless you do it first," which he called a "vicious circle."

But US President George Bush says developing nations must take equal measures to make any deal work, and has shown little enthusiasm for setting goals without them.

G8 leaders are joined on Wednesday by Chinese President Hu Jintao and Indian Prime Minister Manmohan Singh, when the summit is expected to focus on global warming.

China and India say it is up to the heavily polluting developed world to take the lead in the fight against global warming.

"If we agree, then we are in a much better position to discuss with our Chinese and Indian partners and others," Mr Barroso said.

Because of their huge populations and fast-rising economies, China and India are major emitters of greenhouse gases that are blamed for global warming.