Demonstrators hit the streets in major cities across the country Friday — also known as May Day — to support workers' rights, but many demonstrations also protested police brutality in the wake of Freddie Gray's death in Baltimore, and not all protested peacefully.
Here's what has happened across the United States:
Demonstrations turned violent in Seattle after night fell, with police reporting that protesters hurled rocks and wrenches at officers and damaged 25 vehicles. Police reported that an "explosive device" was thrown at officers, and a trash bin was pushed down a hill toward police.
Three officers were injured, two seriously enough that they were taken to a hospital, Seattle police said on Twitter. At least 16 people were arrested Friday night, police said.
"Tonight we saw assaults on police officers and senseless property damage, which cannot be tolerated," Seattle Mayor Ed Murray said in a statement. "Those who are violent will be arrested. We will work to disperse groups that are threatening the safety of our residents and businesses."
The march, which had been billed as an anti-capitalist demonstration, left Seattle Central College at around 6:30 p.m. local time, and rocks were thrown at police about an hour later, NBC station KING 5 reported. Officers responded with pepper spray.
Police used flash bangs and pepper spray to try and stop protesters from entering Interstate 5 about a half hour later, the station reported.
Earlier Friday, hundreds of people marched in Seattle during May Day demonstration for worker and immigrant rights, NBC station KING5 reported. Peaceful protesters at an event different from the one that led to clashes with police chanted "Seattle stands with Baltimore" and "All night all day, we will fight for Freddie Gray," according to the station.
The Seattle Department of Transportation said some streets were briefly closed and there were mass transit delays as marchers moved through Friday. An earlier "black lives matter" march attracted dozens of people.
A crowd estimated to be more than 1,000 in number marched in Manhattan Friday afternoon to "disarm the NYPD" after the death of Gray and other black men after encounters with the police.
"Cops are killing civilians on a regular basis, simple as that, and it's wrong," protester Jordan Jones told NBC New York. Almost 100 protesters were arrested Wednesday during protests over Freddie Gray's death.
Some protesters shouted at police officers when they were told to get back onto the sidewalk, but no arrests were made Friday night, according to the NYPD.
One Portland, Oregon, police officer was injured by a protester, according to police. Portland Police reported on Twitter that protesters were throwing “projectiles” and “incendiary devices” at officers.
Police used pepper spray on protesters who tried to march on a bridge Friday afternoon and later sheriff’s deputies used stingballs, filled with tiny rubber balls, on protesters who were throwing chairs at police, according to the department.
The May Day protests were bolstered by a group calling itself "Don't Shoot Portland," protesting excessive force by law enforcement, which joined hundreds of other demonstrators in the main rally.
Students from Minneapolis Southwest High School began walking out of classes Friday morning holding banners and chanting, "No justice, no peace, prosecute the police," reported NBC affiliate KARE.
Dozens laid down at an intersection to stage a "die-in." The Minneapolis Public Schools supported the students' decision to exercise their rights and said they wouldn't be disciplined as long as they stayed peaceful.
Also, about 200 supporters gathered outside the Hennepin County Courthouse to support people who charged in connection with December's Mall of America "Black Lives Matter" demonstration, KARE said.
After tense demonstrations this week between protesters and police, people again hit the streets and gathered outside Oakland City Hall, They carried signs that read, "We stand with Baltimore," reported NBC Bay Area.
Protesters said they were not only rallying against police brutality but also speaking out about the high cost of living and wage disparity.
"I am sending a clear message that I don't want the tech businesses here," one protester told NBC Bay Area. “I want them to leave because they are not giving back to the community."
Friday's protest in Philadelphia, dubbed "Philly Is Baltimore" marched on City Hall as police followed on either side of the march, NBC Philadelphia reported.
While mostly peaceful, one officer suffered a bloody lip when he was struck by a hurled bottle as protesters tried to enter the Four Seasons Hotel near Rittenhouse Square. The Philadelphia Police Department applauded their officers for a “job well done” Friday night.