L'Aquila, Italy  - The world's eight richest nations eyed a possible agreement on climate change with developing powers on Wednesday as they gathered for a summit in Italy.

But the summit was set to go ahead without China's President Hu Jintao, who was forced to fly home overnight to deal with ethnic violence in the north-western city of Urumqi.

China, India, Mexico, South Africa and Brazil have agreed to a world goal of limiting climate change to 2 degrees centigrade, German Environment Minister Sigmar Gabriel said shortly before the G8 summit opened in the earthquake-ravaged town of L'Aquila.

Italy, which currently holds the Group of Eight's presidency, is now pushing for the club to endorse that goal for the first time, and to say that global greenhouse-gas emissions should peak by 2020 and fall to at least 50 per cent below 1990 levels by 2050.

Last year, G8 leaders meeting in Japan agreed that emissions should fall by 50 per cent before 2050, but did not say what year they were taking as the starting point of that equation.

The EU, which is the only major world economy to have reduced its emissions since 1990, is pushing to have that year set as the base for a new global agreement on fighting climate change at United Nations talks in Copenhagen in December.

The EU is the only international body to belong to the G8, alongside Britain, Canada, France, Germany, Italy, Japan, Russia and the United States.

On Wednesday morning, the head of the EU's executive, Jose Manuel Barroso, and Swedish Prime Minister Fredrik Reinfeldt, current holder of the EU's rotating presidency, called the G8 summit a "unique chance" to tackle climate change.

"Developed countries should reduce their emissions by at least 80 per cent" by 2050, the two leaders, who are to represent the EU at the summit, wrote in the Svenska Dagbladet daily.

Ahead of the summit, diplomats said that the US and Japan, whose emissions have risen by some 18 per cent since 1990, were reluctant to back the 1990 base year and the 2-degree goal, saying that such precise targets should only be defined in Copenhagen.

On Thursday, G8 leaders were set to meet with counterparts from Brazil, China, Egypt, India, Mexico and South Africa to debate climate change, world trade and support to farmers in poor states.

But China's Hu was forced to skip the summit to return home and deal with the outburst of ethnic violence in the province of Xinjiang which has left at least 156 people dead and 1,080 injured.

China, which by some estimates is already the world's greatest atmospheric polluter, is seen as key to any climate deal.

The EU reacted to the violence in Xinjiang by issuing a statement saying that it "deplored" the deaths and called on the Chinese authorities to respect the rights of all those arrested.

G8 leaders were also set to debate the nuclear programmes in Iran and North Korea and the strengthening of financial regulation.

The summit was moved to L'Aquila in a move of solidarity after an earthquake ravaged the mediaeval city on April 6. It had originally been planned for the island of La Maddalena, off Sardinia.(dpa)