A photo shared on Twitter by the Portland Police Department shows burned debris outside the Portland Police Association building in Northern Portland.
Police said some 40 people gathered outside PPA headquarters and lit wood debris on fire. Officers cleared the area to make way for fire officials to put out the flames.
In the photo, the words "Nazis work here," can be seen scrawled on the side of the building.
Portland police said some people were periodically blocking traffic on North Lombard St. near North Campbell Ave. No arrests were made and no injuries were reported.
Fox News could not reach PPD or PPA for comment.
Portland has been the site of ongoing unrest between law enforcement and anti-police protesters. Tensions reached a peak over the summer amid nationwide police protests sparked by the death of George Floyd in Minneapolis.