Police have detained over 400 protesters who had broken off a peaceful demonstration to torch police vehicles and smash shop windows.

Toronto Police Sergeant Tim Burrows told the media on Sunday that 412 people had been arrested for the destruction on Saturday.

The police had to resort to tear gas and pepper spray to fend off the violent protesters, who tried to move toward the security pickets surrounding the Group of 20 Summit site.

Protests started on Friday in Toronto, where at least 2,000 people, mostly young and many appearing to be college students, took to the streets.

Some protesters, holding posters that read "Do You Want to Starve? We Need to Eat Too," told Xinhua that they were protesting against the high government spending on the hosting of the event.

The two-day summit is estimated to cost some 2 billion Canadian dollars (1.93 billion U.S. dollars), far exceeding the original budget of over 100 million Canadian dollars (96.57 million U.S. dollars). More than half of the sum is being spent on security.

The demonstration remained mostly calm and peaceful. There were a few minor confrontations and skirmishes between the protesters and police.

Hundreds of police officers, many wearing helmets and holding anti-riot shields, are guarding the summit venue and patrolling the roads leading up to the venue in cars, and on bicycles and horseback.

It is the first time for G8 and G20 Summits, two important international forums, to be held back to back in one country.