Civil unrest flared and curfews were imposed in several major US cities on Saturday as demonstrators took to the streets to vent outrage at the death of a black man shown on video gasping for breath as a white Minneapolis policeman knelt on his neck.

From Los Angeles to Miami to Chicago, protests marked by chants of "I can't breathe" - a rallying cry echoing the dying words of George Floyd - began peacefully before turning unruly as demonstrators blocked traffic, set fires and clashed with riot police, some firing tear gas and plastic bullets in an effort to restore order.