Protestors had gathered in the Pearl District in downtown Portland around 8:30 p.m., but cops quickly warned anyone who blocked the streets would be arrested.
At around 9:20 p.m., cops said on Twitter they were setting up a perimeter around the demonstrators and detaining them.
But they said the detention was temporary and that protestors would be escorted out “one at a time.”
A crowd stood outside the perimeter chanting “let them go,” according to OregonLive, which also reported cops pepper-sprayed two demonstrators.
The detained protesters were released after being photographed individually by the police; it was unclear if any were charged with crimes.
Ongoing anti-police protests turned violent on Thursday when rioters smashed windows near a federal court and set fires. Police responded with tear gas and smoke bombs to drive away the crowds, the outlet reported.
Meanwhile, suspected rioter Darby Howard, 22, spent another night in jail after being arrested twice on Thursday, Fox News reported.
Howard allegedly caused more than $1,000 in vandalism damage at the downtown Wells Fargo Center Friday afternoon by smashing up a flat-screen TV and a glass sliding door; police say he then punched a cop in the head while they tried to arrest him.
Released Friday night, he was quickly re-arrested for allegedly smashing a window at the downtown courthouse using a Lime rental scooter, OregonLive.com reported.