Thousands of Canadian police have thrown a tight security net over eastern Ontario province, as world leaders begin arriving for key summits focused on economic recovery and development.
In one of the North American country's largest ever security operations, some 20,000 police have been deployed in the city of Toronto and the exclusive lakeside community of Huntsville, some 225 kilometres to the north.
Leaders from the Group of Eight leading economies began flying in one by one to Toronto airport, where they were met on the runway by dignitaries and an honor guard of Canada's iconic scarlet-clad Royal Canadian Mounted Police.
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They were to hold talks on Friday in Huntsville before joining up with leaders and senior officials from developed and emerging nations to form the G20, which meets in Toronto on Saturday and Sunday.
In a huge operation costing a billion dollars, police barricaded Toronto's streets with wire fences and miles of concrete blocks, while helicopters clattered overhead.
Many schools and businesses were closed, and the main Union Station partially shut.
Demonstrations
Protestors are planning days of demonstrations to focus world attention on issues from the environment to the rights of indigenous peoples.
For the second day in a row, police said they halted a potential threat, when the driver of a car laden with home-made weapons was arrested near the downtown Novotel hotel, less than a mile from the G20 convention centre.
The silver Hyundai, topped with a riveted steel roof container was found to contain five fuel canisters, a chain-saw, a home-made crossbow, and arrows.
"The design of the vehicle gave us some concern," constable Hugh Smith told reporters, confirming a man in his mid-50s, had been arrested.
Tensions had been running high since Wednesday, when Canadian authorities said they had uncovered a plot to bomb the summit. A 37-year-old Toronto man and his common-law wife have been charged with possession of explosives.
Among the first leaders to arrive was Chinese President Hu Jintao, who is combining the visit with a formal state visit to Canada.
British Prime Minister David Cameron and Italian Prime Minister Silvio Berlusconi arrived Thursday, followed by Russian President Dmitry Medvedev flying in just hours after White House talks.
Wayne Swan will represent Australia, in his new role as Deputy Prime Minister.
Focus on security and finance
The G8 summit will focus on development and security, tackling issues such as peace-making, maternal health and international crime. Six African leaders will also participate.
The G20 talks will focus more on shoring up recovery as the world economy emerges from its worst crisis in decades.
Ahead of the summits, Cameron urged G20 and G8 nations to start delivering on their pledges.
"Too often these international meetings fail to live up to the hype and to the promises made," he wrote in an editorial in Canada's daily Globe and Mail.
"So the challenge for the upcoming G8 and G20 is to be more than just grand talking shops."
A leaked draft of the final G20 communique, obtained by the environmental group Greenpeace, warns "the recovery is uneven and fragile, and unemployment remains at unacceptable levels."
The talks could also flare into a row between Europe and the United States, with Washington urging its European allies not to cut government spending before recovery is assured, fearing it could trigger a double-dip recession.
German Chancellor Angela Merkel, who has been criticized for aiming to slash spending in Europe's top economy by some 80 billion euros (98 billion US dollars), said she expected "fruitful" but "contentious" discussions here.
Merkel has insisted deficits must be cut in the wake of the eurozone debt crisis that forced Berlin to stump up the lion's share of a rescue mechanism despite fierce voters opposition.
The G20 leaders will also discuss contentious moves to slap new levies on banks to help fund future crisis, with observers saying an agreement remains elusive.
Japan's new centre-left Prime Minister Naoto Kan will make his international debut at the summits in Canada, just three weeks into his job.
"Japan in recent years has had a different prime minister every year," Kan said in an interview with public broadcaster NHK. "Japan's politics and diplomacy have become weak because of it."
