"To those on SW 4th Avenue outside of City Hall. This gathering has been declared a riot. All persons near SW 4th Avenue and SW Madison Street must disperse by travelling to the SOUTH and WEST. You are ordered to disperse immediately," Portland police said on Twitter.
The law enforcement warned in a follow-up tweet that non-compliance might result in "citation or arrest, and may subject you to the use of tear gas, crowd control munitions, and/or impact weapons."
According to local media reports, at least 100 protesters gathered near the city hall and some of them intruded into the building and sprayed graffiti on the walls. Six people reportedly ended up arrested.
On Tuesday, another public gathering near a Portland police association building was declared a riot as protesters set the building on fire. Police intervened and officers were thrown bottles and other objects at. Several people were arrested as a result.