Police said that 605 protesters had been arrested by late afternoon. The running tally did not include the dozens seen detained by a Reuters witness just blocks away from where the Group of 20 leaders wrapped up talks focussed on fixing the ills of the global economy.
The standoff lasted more than five hours, from the late afternoon through to the late evening, as hundreds of police in full riot gear hemmed in protesters at a normally busy downtown intersection. A heavy downpour and a severe thunderstorm warning added to the drama as the standoff continued until 9:43 p.m. (2:43 a.m. BST).
"We had evidence of Black Bloc (anarchist) people, we had people donning masks in that very group, that's exactly how everything started yesterday," said Staff Sergeant Jeff McGuire in explaining why police opted to move against the protesters.
The operation ended abruptly after a heavy downpour, and police released most of the crowd unconditionally, McGuire told reporters. He could not confirm the number arrested.
Earlier, police confronted another group of protesters and fired tear gas for a second straight day.
That clash occurred after hundreds of protesters marched on a temporary detention centre for demonstrators arrested in Saturday's riots. Witnesses saw at least two muzzle blasts, and a police spokeswoman confirmed that "individual applications of tear gas" were fired on the crowd. The blasts are typically used against individuals at close range.
During Saturday's violence police used tear gas against the public for the first time ever in Canada's most populous city.
Among those detained, on charges ranging from mischief to assaulting police, were four people who climbed through the sewer system and emerged near the lock-down area where world leaders were attending the summit.
About 70 people also were detained after police raided the University of Toronto's downtown campus. Police said they seized weapons, including bricks, rocks and sticks.
A local TV station said that four of its reporters were also among those arrested at the Sunday evening standoff.
"Police are continuing to arrest people who engage in criminal activity," said police spokeswoman Jenn Geary. "Media are treated just the way anyone else is. If they breach security they're going to be arrested."
Protesters said police were being heavy-handed, using tactics that instigate violence rather than quell it. They also criticized the media for focussing coverage on violent clashes rather than the broader peaceful marches.
"This is the criminalization of dissent," said Chelsea Flook, with the Toronto Community Mobilization Network, just after police raided a protester convergence place run by the group in search of members of the Black Bloc, which police say instigated the riots over the weekend.
Black Bloc are anarchists who wear black clothing and ski masks to avoid being identified as they attack police and public property. They meld into over-all protest groups and often work to create riot situations.
The weekend violence started on Saturday afternoon after groups of masked anarchists broke away from a larger, peaceful demonstration against the summit of rich and emerging economies.
Protesters, many dressed in black gear, smashed windows of downtown stores and banks and torched police cars.
Anti-G20 groups started demonstrating in Toronto before the summit, which followed a smaller meeting of Group of Eight industrial nations in a resort town north of Toronto. The security bill is set to come in at about $1 billion (644 million pounds).
Such international meetings have been the target of protest groups for years, including demonstrations that disrupted trade talks in Seattle in 1999.
(Additional reporting by David Ljunggren, Claire Sibonney and Janet Guttsman; Editing by Mario Di Simine and Chizu Nomiyama)