Portland police said they arrested 14 people overnight after officers were hit by rocks, bottles and paint balls, following violent clashes between rival groups of demonstrators that roiled the city's downtown area earlier in the day.
Police said they declared a riot just before midnight on Saturday after a group of about 250 people, many of them wearing black and carrying shields, helmets and gas masks, tried to march on a government building that has often been the scene of violence during nearly three months of nightly protests.
Crowd control munitions were used, but not tear gas, the police department said in a statement on Sunday.
Demonstrations against racism and police brutality have swept the United States since the death in May of George Floyd, a 46-year-old Black man who died after a Minneapolis police officer knelt on his neck for nearly nine minutes.
Earlier on Saturday there were scuffles in downtown Portland between anti-racism protesters and right-wing demonstrators. Participants clad in body armor and helmets traded punches and blasts of pepper spray as police officers mostly looked on, according to video of the clashes posted on social media.
President Donald Trump's administration in July deployed federal forces to deal with the protests in Portland. On Friday, he denounced the demonstrations as "crazy" and said cities run by Democrats had descended into chaos. Portland Mayor Ted Wheeler is a Democrat.
Portland police said this week that they have declared a riot at least 18 times since May 29.
On Sunday they said the 14 people arrested were booked into jail on charges including rioting, assaulting a public safety officer, disorderly conduct, and resisting arrest.