"After several orders to disperse, police have used less lethal munitions to effect arrests and move the crowd," the department said via Twitter.
Officers continue "taking projectiles," Portland police said. They added that the crowd has been advised "this is an unlawful protest" after extensive damage to property.
Portland is experiencing the third day of demonstrations following Republican Donald Trump's victory in the November 8 presidential election. At least three individuals have been detained hours after the peaceful demonstration turned into what police classified as a riot.