Several dozen protesters, many using bandanas to cover their faces, began clashing with police in downtown Seattle around 7 p.m., hours after a peaceful immigrant-rights march ended Wednesday evening.
Protesters began by spraying Phoenix Jones and other costumed Rain City Superheroes with silly string. Shortly after that, the window at Sun Liquor was smashed.
The march then wound its way downtown on Pike Street towards the downtown retail core, where demonstrators began shoving and attacking reporters as they provided live on-air reports from the event.
Shortly after that, demonstrators ignited a smoke device, spewing orange pinkish smoke throughout the block.
After demonstrators began damaging property, throwing fireworks and rocks at officers, police formed a line to prevent the marchers from moving any further into the retail core or on to the Interstate 5 on-ramps.
Protesters then began throwing metal rods and full water bottles at officers and business windows, and officers moved in and made arrests.
Protesters threw rocks and bottles at police officers and news crews. As they moved through downtown Seattle to another neighborhood, they flung construction street barriers, trash cans and newspaper bins on the streets in an attempt to stop police officers.
Watch: Protesters, police clash in streets of Westlake
Windows of businesses were broken and vehicles with people in them were banged around.
Police used their bikes to shield businesses and eventually began to use pepper spray and "flash bang' grenades - releasing a flash of light, smoke and a loud noise - to disperse the crowd. But that pushed the group to another nearby neighborhood, and they left a wake of overturned trash cans and debris on the street.
In all, 17 people were arrested for various offenses including property destruction and assault.
Eight officers sustained injuries, mostly bumps and bruises with the exception of one female officer who was struck in the knee by a fist-sized rock.
A woman driving by the scene of one of the protests was injured when a protester hurled a glass bottle at her car, shattering her window. The woman sustained cuts from broken glass and was treated at the scene by medics.
Officers endured a barrage of rocks and bottles throughout the melee until the crowd finally did disperse around 9 p.m.
Mayor Mike McGinn said he was disappointed in the violence.
"We're a bigger and better city than this. I look at this and I am disappointed that this is the picture the world sees of us," he said.
The violence stemmed from a march that billed itself as an "anti-capitalism" protest.
This is the second year in a row violence has broken out during May Day in Seattle. Last year, anarchists broke windows of store fronts, including Niketown, and vehicles and used smoke bombs. Protesters also targeted a federal building, breaking windows and doors.
Olivia One Feather of Covington joined the crowd Wednesday night because she wanted to see how police handled the protest. She said she wasn't impressed, adding that she was pepper sprayed in the face while trying to video record officers.
Of the protesters, she said, "They're doing what we need to do to stand up to ourselves. These are our streets and we have the right to take them."
Many of the protesters are self-described anarchists. A local anarchist website said protesters would attempt to disrupt the day.
After the clashes died down, local residents were seen cleaning up trash left by the protesters.
The violence marred a May Day that immigrant-rights activists hoped would put a focus back on immigration reform. Thousands of people marched about 2 1/2 miles from the Central District toward Seattle's downtown Jackson Federal Building after a May Day rally supporting immigrant rights and labor.
Many carried signs, with messages such as "We are America," and "There are no illegal humans." One sign suggested forgetting about marijuana and instead asking the United States to "Legalize my mom," a reference to Washington's recent legalization of marijuana.
Other demonstrations and rallies in Olympia, Mount Vernon, Spokane, Vancouver, Walla Walla, Wenatchee and Yakima went along peacefully.