More than two dozen May Day protesters were arrested near City Hall in Portland, Oregon, where police canceled a permitted protest over "unsafe conditions," including fires being set and projectiles being thrown.

Portland Police vowed to investigate "criminal acts" carried out during Monday's protest and reached out to the community for tips.

As marchers passed by the Federal Building in Portland, windows were smashed and broken by "anarchists," KOIN reported.

Multiple fires were also reported.

The permitted protest began at 3:00pm local time, but police revoked the permit by 4:15pm, according to KOIN.

Shortly after 5:30pm, Portland Police tweeted that the "riot has subsided." They will patrol Downtown Portland "as things continue to de-escalate."

Fire at SW Morrison/4th - squads of @portlandpolice just rushed forward to put out fire #MayDayPDXpic.twitter.com/qHuI01RE4X — Maxine Bernstein (@maxoregonian) May 1, 2017

May Day marches took place nationwide to support workers and immigrants, as well as to protest President Donald Trump. Portland's began peacefully like the rest of the demonstrations, but a small minority reportedly hijacked the event.

Numerous people have been detained in the area of City Hall. #MayDayPDX Anyone remaining in the area is subject to arrest. — Portland Police (@PortlandPolice) May 2, 2017

Police reported that one of their squad cars was destroyed, according to KOIN. Witnesses reported seeing someone lighting a police cruiser on fire. Footage from KATU seems to corroborate the accounts.

Nearly an hour after the protest was canceled, lingering protesters gathered on a sidewalk near riot police and yelled chants of "Who do you protect, who do you serve?" and calls of "Shame!"

5th/Jefferson is completely blocked. The people arrested are getting some applause from spectators. #MayDayPDXpic.twitter.com/zlLmkAELqB — Everton Bailey Jr. (@EvertonBailey) May 2, 2017

Damage at old Federal Courthouse on SW Broadway #MayDayPDXpic.twitter.com/15eA9jWfFm — Lynne Terry (@LynnePDX) May 2, 2017

The Portland Police cancelled the #MayDay2017 protest because it was a riot. pic.twitter.com/8CTYdvLdyW — BeeNews (@BeeNewsDaily) May 2, 2017