When they arrived, at around 10:20 p.m., police warned those in the area over a loudspeaker to remain on the sidewalk, and "be courteous to your neighbors" because the nearby streets around the police union building were open to vehicular traffic.
"Do not vandalize buildings," police added.
Police said individuals stood on the sidewalks while others blocked N. Lombard Street. They added that the group also used traffic signs to block the street and some climbed onto the roofs of businesses in the area.
Around 11:15 p.m., authorities said that people in the crowd set fire to a billboard located next to the PPA office.
The billboard reportedly read, "WAKE UP AMERICA!" and "THANK YOU PORTLAND POLICE BUREAU," before it was engulfed in flames, according to Oregon Public Broadcasting reporter, Sergio Olmos.
Portland police issued another warning to the crowd minutes later where they threatened to arrest people who engaged in criminal activity.
"Stay off buildings, do not light fires, and remain on the sidewalk. If you engage in criminal activity you could be arrested and subject to use of force to include crowd control agents, impact weapons, and/or tear gas," authorities said.
The crowd began to disperse on their own by 12:15 a.m, according to police. Authorities said they did not interact with the protesters with the exception of a sound truck.
No arrests were made, police added.
The PPA building has become a frequent target during the ongoing protests in the city against racial injustice. Back in August, fires were set near the building which required officers to move in to prevent it from spreading, police said at the time.
In September, a Portland police sergeant was sent to the hospital and at least 24 people were arrested after demonstrators gathered outside the building. The sergeant sent to the hospital was reportedly punched in the face.
Fox News' Danielle Wallace contributed to this report