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Seattle police say five people were arrested in May day protests downtown Monday.

Police asked protesters to leave Westlake Park in downtown Seattle after "increasing tensions and several fights."

Supporters of President Trump, called the "Cowboys," gathered at Seattle's Westlake Park before 4:30 p.m. Shortly after, a group of "Black Bloc" protesters arrived at the park. Officers separated the two groups after they began yelling at each other.

.@seattlepd move in to separate Pro Trump protesters from the Anti #MayDaySea pic.twitter.com/b3FrH6MMHX

— elisa hahn (@ElisaHahnK5) May 2, 2017

An Olympia man, 26, was arrested for throwing a rock just before 6 p.m. A witness said he threw it at President Trump demonstrators.

An Olympia man, 30, was arrested for unlawful possession of a hunting-style knife just before 7 p.m.

A Colorado man, 51, was arrested at about 7:45 p.m. for obstruction.

A Seattle man, 27, was arrested about 8:15 p.m. for obstruction.

A 19-year-old was arrested for misdemeanor theft for stealing another demonstrator's flag.

Nine people were arrested in Olympia for what police called rioting.

Seattle Mayor Ed Murray said the number of people participating in May Day activities in Seattle was a “surprise.”

“This is my fourth May Day as mayor, and it’s the smallest one I have seen … so far." Murray said early in the evening. “We had expected something much closer to the Women’s March than what we saw today.”

According to police, about 1,500 demonstrators marched in the El Comité May Day March for Worker and Immigrant Rights from Judkins Park to Seattle Center earlier in the day There was an anti-war rally and march prior to that.

Related: Q&A history of May Day

The El Comité May Day March for Worker and Immigrant Rights was a large focus for city crews, working to navigate traffic and escort marchers along their route.

Seattle City Councilmember Kshama Sawant made an appearance at the rally at Judkins Park, calling on demonstrators to "demand the right to unionize without retaliation."

The rally was followed by a peaceful, colorful march through downtown Seattle to Seattle Center. Police maintained a significant presence along the route throughout the duration of the permitted event.

Seattleites dealt with street closures and clogged commutes.

Demonstrators stayed on the permitted route and did not make their way onto Interstate 5. Sawant, in an interview last month, voiced encouragement for such types of tactics. But last week, when asked if her comments were misconstrued, she said the march route does not go on I-5.

Numerous unpermitted events included marches by Climate Justice, Working Washington, March on Amazon, UW May 1st Day of Resistance, Stand Against Communism and two May Day Anti-Fascist groups.

Related stories:

Sawant says May Day march route does not go onto I-5

Seattle police prepare for May Day

Seattle May Day rallies and march route