Leaders of the world's most powerful economies began Thursday a two-day G20 summit dominated by a debt crisis which could force Greece from the eurozone. Host President Nicolas Sarkozy of France welcomed heads of state of governments from the world's 20 largest economies at the Palais des Festivals in the French Riveria resort of Cannes. Initial discussions were set to focus on the eurozone debt crisis. Sarkozy and his German counterpart Chancellor Angela Merkel had hoped to reassure their partners by forcing Greece's Prime Minister George Papandreou to quickly implement an EU bail-out deal. He was summoned to pre-summit talks Wednesday and agreed to hasten his planned referendum on the plan, insisting Greece wanted to stay in the euro, but he flew home to find his parliamentary majority evaporating. G20 leaders are also to discuss measures to boost growth as the world threatens to slip back into recession over the instability caused by the eurozone crisis.