Protesters shattered business windows, set bonfires in the streets and vandalized a police car Monday afternoon in downtown Portland as a May Day protest devolved into a short-lived but chaotic riot.

The demonstration began as a city-permitted march featuring impassioned but peaceful rhetoric, but it ultimately was defined by black-clad protesters, fires and property damage. Ninety minutes into the march, police declared the gathering a riot. Officers used flash-bang grenades to disperse the crowd after they pronounced the march illegal, eventually arresting 25 people.

May 1 is International Workers' Day, and protesters from the Philippines to Paris celebrated by demanding better working conditions. The holiday traditionally celebrates laborers' rights but in recent years has expanded its focus in the U.S. to support immigrants.

Arrests

— Ayden Michael Foster-Wysocki, 21: Facing second-degree disorderly conduct charge

— Madhab Pulle, 18: Second-degree disorderly conduct

— Tyler Hans Larsen, 37: Second-degree disorderly conduct

— Luis Marquez, 44: Second-degree disorderly conduct

— Grahme Meneses, 20: Second-degree disorderly conduct

— Jace Anthony Willis, 22: Second-degree disorderly conduct

— Corey Daniel Joe, 42: Second-degree disorderly conduct and assaulting a police officer

— Brianna Borgen, 19: Second-degree disorderly conduct

— Rachel Visco, 34: Second-degree disorderly conduct

— Phoebe Loomis, 33: Second-degree disorderly conduct

— Michell Korin Myers, 19: Second-degree disorderly conduct

— Rylie Wolff, 22: Second-degree disorderly conduct

— Lucy Elizabeth Smith, 35: Second-degree disorderly conduct

— Glenn Allen Silbersdorff, 38: Second-degree disorderly conduct

— Christopher Fellini, 28: Second-degree disorderly conduct

— Frank Martinez, 24: Second-degree disorderly conduct and resisting arrest

— Ian Lawrence Henderson, 28: Second-degree disorderly conduct

— Javier Ivan Reyes, 20: Second-degree disorderly conduct

— Dan Edward Wright, 34: Second-degree disorderly conduct

— Jeff Richard Singer, 29: Second-degree disorderly conduct and interfering with a peace officer

— Taylor James Evans, 24: Second-degree disorderly conduct and interfering with a peace officer

— John Barton Elliott, 26: Second-degree disorderly conduct

— 17-year-old: Riot

— 14-year-old: Riot

— 17-year-old: Riot

Source: Portland Police Bureau

The Oregonian/OregonLive generally doesn't identify juveniles accused of crimes unless they're tried as an adult or face Measure 11 charges.

Police ask business personnel and other people who think they're victims of crimes to call a non-emergency number, 503-823-3333, or file a report online.

A common theme in the widespread U.S. was disapproval of the President Donald Trump, who in his first 100 days has intensified immigration enforcement by pushing for a U.S.-Mexico border wall and a ban on travelers from six predominantly Muslim countries.

In Portland, the afternoon began with a rally in the South Park Blocks, where speakers addressed about 1,000 people in Shemanski Park while a group of self-described anarchists gathered at a distance from the microphones.

One of the more than half-dozen speakers urged the crowd to support workers' rights and unions. A Somali, Muslim woman encouraged people to continue fighting against racism, Islamophobia and other social injustices and to not lose hope.

Police at the periphery of the rally confiscated several sticks, poles and homemade shields — which were in sharp contrast to the more plentiful balloons, banners, costumes and props that otherwise filled the park. Some of the black-clad demonstrators burned small American flags.

Marchers set off after about 90 minutes, chanting as they marched south along the park blocks and turned toward the waterfront. Marchers remained mostly peaceful as they meandered past City Hall and the west side of the Justice Center.

But things turned violent as some in the crowd began throwing rocks and full soda cans at police while the mass moved north on Southwest 2nd Avenue.

Police later said items protesters threw or launched at officers also included fireworks, road flares and smoke bombs. Anarchists also threw at least one Molotov cocktail at officers but didn't hit them, a police spokesman said in an email.

Police in riot gear rolled in after the first objects were lobbed. Shortly after, police declared the assembly "unlawful" and warned that any marchers in the streets faced arrest.

The first of two main flashpoints came shortly after at Southwest 4th Avenue and Morrison Street, where demonstrators lit a large bonfire in the intersection using traffic cones, newspaper and brochure boxes, wood and a pallet. The blaze produced a plume of black smoke that rolled skyward next to a Starbucks and MAX tracks.

Officers rushed the scene, firing flash-bang grenades to disperse the crowd. The flames were quickly extinguished.

Police shortly after declared the demonstration a riot, saying protesters had vandalized a police car, were "attacking" officers and were vandalizing property.

Officers stymied the protest on the west side of City Hall about 10 minutes later, swooping in on protesters from the north and south and taking dozens into custody.

Damage included windows shattered or broken at the Mark O. Hatfield U.S. Courthouse, City Hall, J. Crew, Brooks Brothers, Target, Gus J. Solomon U.S. Courthouse building and Michael Parsons Fine Arts gallery.

A rock was thrown through a window at Goldmark Jewelers, and protesters left a wall and other windows marred by graffiti.

"Why'd they have to do this?" said Kurt Thomas, the building security guard. "The owner's a nice guy, not a corporate store at all."

City Hall was also tagged with graffiti, as was the shuttered Macy's building and other downtown structures. Someone scrawled "Kill Cops" on a Biketown rack, its bicycles' tires slashed.

Police said in a news release Monday night that officers deployed "limited" amounts of less-than-lethal munitions during the riot.

Portland Police Chief Mike Marshman said he's "proud of the professionalism" shown by law enforcement officers and firefighters who "worked to keep the peace in Downtown Portland under very difficult circumstances."

"Unfortunately the actions of the law breakers undermined and covered up the message of the law abiding individuals who worked to peacefully get their message heard on May Day," he said in a statement.

The Portland May Day Coalition, which organized the rally and march, didn't immediately respond to messages seeking comment Monday evening. It did, however, address the day's events on Facebook, saying in part that police "chose to violently escalate a peaceful march."

Today the Portland police chose to violently escalate a peaceful march. The people asserted their (lawful) right to be... Posted by Portland May Day Coalition on Monday, May 1, 2017

The coalition, made up of almost 50 organizations, had released its march route and obtained a city permit for the event.

That route was followed only partway, never formally returning to the park where it began.

A separate group, called the Anarchist Student Union, vowed beforehand to join the event and "do our own thing." It was unclear how many of the anarchists were among those arrested. But the vast majority of the hundreds — possibly thousands — of people assembled participated peacefully.

The 25 arrested include two 17-year-olds and a 14-year-old who each face riot charges, police said. They were released to parents, police said, and the other 22 people arrested were jailed.

Each of the adults arrested face second-degree disorderly conduct charges and traffic citations for failing to obey a police officer, according to police. Police said two adults face interfering with a peace officer charges, one faces an assaulting a police officer charge and another faces a resisting arrest charge.

Portland police released booking photos for adults arrested in a May Day demonstration that was deemed a riot on May 1, 2017.

Elsewhere in the U.S., peaceful protesters flocked to the streets in Chicago. At the White House gates, they demanded "Donald Trump has got to go!"

Three people in Seattle were arrested, one for hurling a rock as pro- and anti-Trump demonstrators faced off. In Olympia, police ordered protesters to disperse, calling them "members of a mob" as some threw bottles, used pepper spray and fired rocks from slingshots at officers. Two officers were injured and 10 people were arrested.

In Oakland, California, at least four were arrested after creating a human chain to block a county building where demonstrators demanded that county law enforcement refuse to collaborate with federal immigration agents.

Despite the West Coast clashes, most nationwide protests were peaceful as immigrants, union members and their allies staged a series of strikes, boycotts and marches to highlight the contributions of immigrants in the United States.

— Jim Ryan

jryan@oregonian.com

503-221-8005; @Jimryan015

The Associated Press and Everton Bailey Jr., Maxine Bernstein, Tony Hernandez, Dave Killen, Stephanie Yao Long and Lynne Terry of The Oregonian/OregonLive staff contributed to this report