A permitted march began around 3 p.m. in Shemanski Park in downtown Portland. Police confiscated sticks and homemade shields from several participants before the event started.
Police report that early in the march, some protesters hurled rocks, fireworks and other projectiles at officers.
A full Pepsi can hit a Portland Fire and Rescue paramedic.
Tear gas and flash bangs were used to disperse protesters after the situation seemed to escalate.
Several storefronts and vehicles were vandalized downtown and multiple fires were started in the streets.
Around 4 p.m. the Portland Police announced that the permit for the march was canceled due to unsafe conditions, and asked participants to leave the area.
Twenty-five people were arrested in Portland during a May Day protest that police say turned into a riot, May 1, 2017.
Amelia Templeton / OPB
What started as a peaceful May Day march through downtown Portland turned into a riot, May 1, 2017
Amelia Templeton / OPB
What started as a peaceful May Day march through downtown Portland turned into a riot, May 1, 2017
Amelia Templeton / OPB
What started as a peaceful May Day march through downtown Portland turned into a riot, May 1, 2017
Amelia Templeton / OPB
What started as a peaceful May Day march through downtown Portland turned into a riot, May 1, 2017
Amelia Templeton / OPB
A large group of anarchists at the back of Portland's May Day march tangled with the police, May 1, 2017.
Amelia Templeton / OPB
Twenty-five people were arrested in Portland during a May Day protest that police say turned into a riot, May 1, 2017.
Amelia Templeton / OPB
Twenty-five people were arrested in Portland during a May Day protest that police say turned into a riot, May 1, 2017.
Amelia Templeton / OPB
Twenty-five people were arrested in Portland during a May Day protest that police say turned into a riot, May 1, 2017.
Amelia Templeton / OPB
Twenty-five people were arrested in Portland during a May Day protest that police say turned into a riot, May 1, 2017.
Amelia Templeton / OPB
Twenty-five people were arrested in Portland during a May Day protest that police say turned into a riot, May 1, 2017.
Amelia Templeton / OPB
Portland Police repeatedly used flash bang grenades and tear gas against the marchers, May 1, 2017.
Amelia Templeton / OPB
Portland Police clashed with the "black bloc" outside the Pioneer courthouse mall where the anarchists lit a fire, May 1, 2017.
Amelia Templeton / OPB
Portland Police clashed with the "black bloc" outside the Pioneer courthouse mall where the anarchists lit a fire, May 1, 2017.
Amelia Templeton / OPB
Twenty-five people were arrested in Portland during a May Day protest that police say turned into a riot, May 1, 2017.
Amelia Templeton / OPB
Twenty-five people were arrested in Portland during a May Day protest that police say turned into a riot, May 1, 2017.
Amelia Templeton / OPB
Twenty-five people were arrested in Portland during a May Day protest that police say turned into a riot, May 1, 2017.
Amelia Templeton / OPB
Anarchists slashed tires and vandalized the BIKETOWN station at Pioneer Courthouse Square, May 1, 2017.
Amelia Templeton / OPB
Anarchists slashed tires and vandalized the BIKETOWN station at Pioneer Courthouse Square, May 1, 2017.