Leaders of the Group of 20 (G20) major economies on Saturday afternoon started their fourth summit since 2008 in Canada's largest city Toronto, seeking ways to consolidate the world's fragile recovery from deep recession and address the root causes of the global economic crisis.

This is the first G20 summit in its new capacity as a premier forum for international economic cooperation and policy coordination, as determined at the previous summit in Pittsburgh, the United States last September.

At an official welcome and reception ceremony held in Royal York Hotel of Toronto, Canadian Prime Minister Stephen Harper and his wife Laureen greeted other G20 leaders and spouses one by one, shaking hands and posing for pictures on red carpet.

A plenary session is scheduled for Sunday morning in the Metro Toronto Convention Center, the main venue of the summit.

Under the theme of "Recovery and New Beginnings," the Toronto summit is expected to focus on recovery from the global economic and financial crisis and the implementation of commitments from the previous G20 summits -- the first in Washington in November 2008 and second in London in April 2009.

Major topics to be discussed during the summit include securing recovery and restoring balance to public finances, reforming the global financial system, strengthening international financial institutions, and liberalizing trade and investment.

Observers say that while the G20 leaders share the common objective of laying the foundations for sustainable and balanced growth for the future, they also differ on certain approaches and practices, particularly on some thorny issues like economic stimulus exit strategy and taxation of banks.

This year's G20 summit took place just hours after the conclusion of the annual Group of Eight (G8) summit in Huntsville, Canada's Muskoka region, reflecting increased interaction and enhanced cooperation between the two previously separate international forums.

However, the G8 leaders on Saturday clearly rejected the idea of disbanding their over-three-decade-old group and letting the G20 take over its role in international affairs.

At a closing press conference for the G8 summit, Harper, whose country holds the rotating G8 presidency this year, said that although the G20 has done a magnificent job in dealing with the financial crisis, it also has limits, and that the G8 will remain "equally vital" as the G20 and other key international bodies and forums.

The first ever back-to-back hosting of both events gave Canada, a member of both groups, unprecedented media exposure and global attention.

However, a major anti-G20 protest involving thousands of people on Toronto's downtown streets, which eventually turned violent with some rioters burning police vehicles and smashing windows of roadside businesses, marred the pre-summit atmosphere earlier on Saturday afternoon.

An angry Toronto Mayor David Miller called the small group of rioters "thugs" and "criminals" that deserved legal punishment.

Security measures for the summit, including fences around the summit venues and around-the-clock police patrol in core areas, cost an estimated 1.2 billion Canadian dollars (1.16 billion U.S dollars), though mostly paid by the Canadian federal and Ontario provincial governments.

The G20 members, namely Argentina, Australia, Brazil, Britain, Canada, China, France, Germany, India, Indonesia, Italy, Japan, Mexico, the Republic of Korea, Russia, Saudi Arabia, South Africa, Turkey, the United States and the European Union, account for 90 percent of global output, 80 percent of world trade and two-thirds of the world's population.

Also participating in the summit are heads of international organizations including the United Nations, the World Bank, the International Monetary Fund (IMF) and the Organization for Economic Cooperation and Development, as well as heads of state or government from a few non-G20 countries including Ethiopia and Vietnam.

Chinese President Hu Jintao, who had participated in all the previous G20 summits, arrived in Toronto on Friday afternoon for this one.

China said earlier that it had four main expectations for the current summit, including enhancing communication and coordination on macro-economic policies between G20 members in the wake of the European sovereign debt crisis, pushing for the completion of the IMF quota reform and the improvement of the international financial system, providing support to the UN Millennium Development Goals, and fighting trade protectionism and promoting the completion of the Doha round negotiations.