Protesters at a May Day march in Seattle, Washington clashed with police during what law enforcement called "a riot" on Friday. Officers deployed flashbangs and pepper spray to try and get the crowd under control.

Hundreds of demonstrators took to the streets Friday to participate in pro-worker, anti-police-brutality rallies, as well as one that was billed as anti-capitalist. According to the Seattle Times, one protester broke a window and others threw rocks at police before law enforcement responded with flash bangs.

Pepper spray flash bangs craziness. Police took back the street #MayDaySea#Videopic.twitter.com/jY9XF1ANZ7 — Lauren Frohne (@laurenfrohne) May 2, 2015

"As we continue to witness acts of violence from protesters, we urge folks on Capitol Hill to exercise caution," said Mayor Ed Murray in a statement. "Seattle Police are advising that businesses on Broadway and other Capitol Hill streets should take reasonable precautions to protect their employees and customers. Police will continue to work to protect people and property in the area, and will make arrests when necessary."

Seattle police officer injured in May Day violence. #Q13FOXpic.twitter.com/Vbmfai6aeb — Thomas Brock (@Q13FoxNews_Tom) May 2, 2015

Three officers have been injured at the scene of a melee at Broadway and Howell, the Seattle Police Department tweeted, two of which were hurt seriously. A total of fifteen people have been arrested across the city, police said.

One protester has reportedly thrown a burning object into a vehicle. Police said fires have been ignited at Seattle Plaza and that 25 vehicles have been damaged.

Anarchists light a flag and spray paint the silver sculpture outside Seattle Central #MayDaySeapic.twitter.com/TfA6CVtvNr — Bettina Hansen (@bettinahansen) May 2, 2015

Police tweeted that an "explosive device" was thrown at officers and said the situation has escalated into a riot.

"This is no longer demonstration management, this has turned into a riot" -Captain Chris Fowler. #MayDaySea — Seattle Police Dept. (@SeattlePD) May 2, 2015

Meanwhile, video surfaced of individuals breaking windows as they made their way through the city.

The Seattle Times reported that earlier in the day, a Black Lives Matter march planned to meet up with the May Day March for Workers and Immigrants Rights. Earlier in the day, police said they were concerned about a third group of self-proclaimed anarchists who might try to cause chaos in the city.

The line has been drawn at Broadway and Pine. Flash bangs and pepper spray dispersing crowd. #MayDaySeapic.twitter.com/INoM3K3vY4 — Jon Humbert (@jonhumbert) May 2, 2015

In this video, some of the masked protesters can be seen marching and chanting.

NOW: Broadway at Thomas, anti-capitalists on the move and chanting. pic.twitter.com/3TPmlmu0Iz — Janet Kim (@JanetKimTV) May 2, 2015

For most of the day, the marches were peaceful even though protesters disrupted traffic at times.

When confrontation first broke out between police and protesters, officers were reportedly hit with flags and sticks.

Rewind: the moment the police moved in. Dropped bikes. Protesters hit cops with their flag sticks #MayDaySea#Videopic.twitter.com/dwLyIOLtYF — Lauren Frohne (@laurenfrohne) May 2, 2015

Seattle Police Captain Chris Fowler explained the situation to a reporter on the ground.

Amid the chaos, some helped clean up what others made a mess of.