ATLANTA — Protests took a violent turn in several U.S. cities over the weekend with demonstrators squaring off against federal agents outside a courthouse in Portland, Oregon, forcing police in Seattle to retreat into a station house and setting fire to vehicles in California and Virginia.

A protest against police violence in Austin, Texas, turned deadly when a witness says the driver of a car that drove through a crowd of marchers opened fire on an armed demonstrator who approached the vehicle. And someone was shot and wounded in Aurora, Colorado, after a car drove through a protest there, authorities said.

The unrest Saturday and early Sunday stemmed from the weeks of protests over racial injustice and the police treatment of people of color that flared up after the May 25 death of George Floyd in Minneapolis. Floyd, who was Black and handcuffed, died after a white police officer used his knee to pin down Floyd's neck for nearly eight minutes while Floyd begged for air.

In Seattle, police officers retreated into a precinct station early Sunday, hours after large demonstrations in the city’s Capitol Hill neighborhood. Some demonstrators lingered after officers filed into the department’s East Precinct around 1 a.m., but most cleared out a short time later, according to video posted online.

At a late-night news conference, Seattle police Chief Carmen Best called for peace. Rocks, bottles, fireworks and mortars were fired at police during the weekend unrest, and police said they arrested at least 45 people for assaults on officers, obstruction and failure to disperse. Twenty-one officers were hurt, with most of their injuries considered minor, police said.

In Portland, thousands of people gathered Saturday evening for another night of protests over George Floyd’s killing and the presence of federal agents recently sent to the city by President Donald Trump. Protesters breached a fence surrounding the city’s federal courthouse building where the agents have been stationed.

Police declared the situation to be a riot and at around 1:20 a.m., they began ordering people to leave the area surrounding the courthouse or risk arrest, saying on Twitter that the violence had created “a grave risk” to the public. About 20 minutes later, federal officers and local police could be seen attempting to clear the area and deploying tear gas, however protesters remained past 2:30 a.m., forming lines across intersections and holding makeshift shields as police patrolled and closed blocks abutting the area. Multiple arrests were made, but it wasn’t immediately clear how many.

In the Texas capital of Austin, a protester was shot and killed Saturday night after witnesses say he approached a car that had driven through a march against police violence. In video streamed live on Facebook, a car can be heard honking before several shots ring out and protesters start screaming and scattering for cover. Police could then be seen tending to someone lying in the street.

Michael Capochiano, who attended the protest, told the Austin American-Statesman that the slain protester had a rifle and that the car's driver fired several shots at him before speeding away. Police said the driver was detained and was cooperating with investigators.

Austin police haven’t identified the slain protesters but the man’s mother said his name was Garrett Foster, The Dallas Morning News reported.

Sheila Foster said her son was pushing his fiancée’s wheelchair across the intersection when the man drove through the march.

In the Denver suburb of Aurora, Colorado, meanwhile, a protester shot and wounded someone after a car drove through a crowd marching on an interstate highway, police said. The wounded person was taken to a hospital in stable condition. Police didn’t release many details about the shooting, including whether the person who was shot had been in the car. Police said on Twitter that demonstrators also caused “major damage” to a courthouse.

Protesters in Oakland, California, set fire to a courthouse, damaged a police station, broke windows, spray-painted graffiti, shot fireworks and pointed lasers at officers after a peaceful demonstration Saturday evening turned to unrest, police said.

In Virginia's capital, Richmond, a dump truck was torched as several hundred protesters and police faced off late Saturday during a demonstration of support for the protesters in Portland. Police declared it to be an “unlawful assembly” at around 11 p.m. and used what appeared to be tear gas to disperse the group. Five people were arrested in the incident and charged with unlawful assembly. A sixth person was also arrested and charged with rioting and assault on a law enforcement officer.

In downtown Atlanta on Sunday, federal agents examined damage to an Immigration and Customs Enforcement facility where windows were shattered late Saturday. The FBI and the Department of Homeland Security, FBI spokesman Kevin Rowson said in an email. No arrests had been announced.

And in Baltimore, people from a group of nearly 100 demonstrators spray-painted anti-police messages on a Fraternal Order of Police building and adjacent sidewalks on Saturday night, The Baltimore Sun reported.

Associated Press writers Gillian Flaccus and Sara Cline in Portland, Oregon, and Sally Ho and Chris Grygiel in Seattle contributed to this report.