9:06 p.m. update: Police used flash bangs and pepper spray as officers and protesters clashed late Wednesday as a May Day rally turned violent in Seattle.
Protesters threw several objects, possibly rocks and other items, at police officers and news crews.
Officers responded by using flash bangs and pepper spray and using their bikes as shields. A few people were seen taken into custody.
Earlier, thousands of people marched peacefully through downtown.
The violence broke out later in the evening after a separate march started at the Capitol Hill neighbourhood. Many of the protesters are self-described anarchists.
Police have made several arrests after apparent anarchists and May Day marchers arrived in downtown Seattle, screaming, blowing whistles, lighting flares and leaving a broken window in their wake.
Protesters met at Seattle Central Community College at the busy intersection of Broadway and Pine and then spilled into the street, blocking traffic.
KIRO 7 Eyewitness News reporter Essex Porter said at first there appeared to be more spectators than participants and the gathering seemed to be more of a party than a rally.
But as the crowd began to move, flares were lit and the crowd became noisy as it made its way toward downtown on Pike street, flanked by police officers.
Seattle police tweeted that someone in the crowd may have broken a window at Sun Liquor on East Pike and Belmont, and people clad in black, with their faces covered, were seen in the mix.
As the group of several hundred people moved north on Sixth Avenue after turning off of Pike Street, police said some in the group were throwing metal bars and water bottles at businesses' windows.
A KIRO 7 News crew was surrounded by rowdy protesters. They spit and sprayed Silly String on KIRO 7 reporter David Ham and hit his photographer.
Police said there was no permit for the rally, and no information about where they were headed, but their final destination was Westlake Plaza.
It was there that at least two people were taken into custody. One protester's hands and feet were restrained as the crowd became angry.
As the crowd's fervor intensified, metal pipes were thrown from the crowd onto cars and people.
More details to come.