Leaders from the Group of 20 (G20) rich and emerging nations arrived on Wednesday in London for a summit that aimed to reach an agreement over pulling the world out of the worst crisis since the 1930s.

Chinese President Hu Jintao (4th L, 1st row) and other leaders attending the Group of 20 summit pose for group photos during a reception hosted by Queen Elizabeth II in London, Britain, on April 1, 2009. [Xinhua]

Leaders were busy holding bilateral talks with one another and called for unity to handle the crisis.

But differences are visible, with the United States and the United Kingdom pitted against the European countries over the balance between extra financial stimulus and the need for regulation, as emerging countries call for a bigger say.

French President Nicolas Sarkozy, who has threatened to walk out of the summit, said yesterday that neither France nor Germany was satisfied with current proposals for an accord at the summit and warned that he would not accept any "false compromises".

"I will not associate myself with a summit that would end with a communique made of false compromises that would not tackle the issues that concern us," he told Europe 1 radio in an interview.

"Regulation is at the heart of the debate that we are going to be holding during these hours," he said.

US President Barack Obama and British Prime Minister Gordon Brown, who is struggling to bridge the G20 summit gap, played down the differences but not the scope of the crisis that the summit will have to confront.

"Make no mistake, we are facing the most severe economic crisis since World War II, and the global economy is now so fundamentally interlinked that we can only meet this challenge together," Obama said.

But he insisted that while the summit had a duty to produce "the most substantive outcome possible", the "separation between the various parties has been vastly over-stated".

Obama has said stimulus and regulation are needed but the US could not shoulder all the responsibility for creating new growth.

German chancellor Angela Merkel voiced her concern before leaving Berlin.

"I am going to London with a mixture of confidence and concern. Concern on one hand on whether we can really react to the serious situation ... Confident, however, that ... we cannot stick our heads in the sand," she said.