Seattle police say nine people including a teenage girl were arrested and five officers were injured during anti-capitalist protests on May Day.
The protestors who suffered from police violence were charged with obstruction, assault and property destruction.
Every year on May 1 protesters gather to attract attention on labor and immigration issues and police violence.
Dozens of people dressed in black had gathered at a downtown park following a peaceful, permitted march by advocates for workers and immigrants. They marched through downtown and were later pushed south by officers in riot gear on bikes.
Police used pepper spray to disperse the protesters, saying that rocks, flares and bricks were thrown at officers downtown.
In posts on the social media website Twitter, the Seattle police department said one officer had suffered a cut to the head as protesters hurled Molotov cocktails, another was hit by a rock, and a third officer was bitten, apparently by a protester.Injuries suffered by two more officers were not detailed.
"Nobody has been seriously injured," police chief Kathleen O'Toole said after the unrest subsided, adding, "Once assaults started and property damage started, we took action. It's that simple."
Many participants on Sunday carried signs and flags as they made their way through the city under sunny skies.
Seattle Police escorted the marchers for the permitted parade. There was also a concert at Seattle's Westlake Park.
Later in the evening an anti-capitalist march was slated to begin in a downtown park. Authorities haven't issued a permit for that gathering.
The anti-capitalist demonstrators, who didn't have a permit from city officials, then started marching through the streets. They carried signs including one that said, "We Are Ungovernable."
Mayor Ed Murray claimed that the crowd was "different" than those who had attended an earlier peaceful May Day immigrtion march and blamed them for the senseless violence.
Police used "blast balls" to disperse the crowd.
A similar violence occured on last year’s May Day, when police used pepper spray and flash grenades against the protestors. Sixteen people were arrested and three officers were hurt which similarly erupted after a day of peaceful demonstrations.