Black-clad demonstrators have broken off from a crowd of peaceful protesters at the global economic summit in Toronto, setting fire to police vehicles and smashing windows with baseball bats and hammers.
Police arrested more than 400 people.
They used shields, clubs, tear gas and pepper spray to push back the rogue protesters who tried to head south toward the security fence surrounding the perimeter of the Group of 20 summit site.
Some demonstrators hurled bottles at police.
Toronto police chief Bill Blair said: “We have never seen that level of wanton criminality and vandalism and destruction on our streets.”
The group – wearing black balaclavas – shattered shop windows on several blocks, including at police headquarters.