London  - Leaders of the world's big economic powers are gathering Wednesday in London ahead of a landmark crisis summit to combat the worldwide recession and revamp the global financial system.

The summit of the leaders of the Group of 20 (G20) major industrialized countries and emerging economies is to open with a reception at Buckingham Palace and a working dinner at the residence of British Prime Minister Gordon Brown, the G20 host.

Many of the leaders attending the summit, which is to be held in London's vast new trade centre on the banks of the River Thames, are expected to hold a series of bilateral meetings Wednesday.

The leaders, who include the government heads of the United States, France, Germany, Canada, Japan, China, India and Brazil, are to get down to the hard work of hammering out measures to address the biggest economic crisis since World War II.

Overhanging the summit is the threat of violent protests, with a heavy police presence on the streets and many businesses in London's financial centre boarding up windows.

Representing countries that make up about 85 per cent of the world's economic activity, the G20 leaders are expected to sign off Thursday on a series of steps to include improving national economic co-ordination and tightening global financial market supervision. (dpa)