PORTLAND, Ore. — A fire inside a police union building led authorities in Portland to declare a riot and force protesters away from the offices as violent demonstrations continue in the city that had hoped for calm after federal agents withdrew more than a week ago.

Three officers were hurt, including two who were taken to a hospital, during efforts to clear a crowd of several hundred people outside the Portland Police Association building late Saturday, police said in a statement. The two hospitalized officers have since been released.

Rallies had been held earlier in the afternoon and evening throughout the city, including at Peninsula, Laurelhurst and Berrydale parks, local media reported.

Police said a group from Peninsula Park marched to the Portland Police Association building, which is located about 5 miles north of the federal courthouse that had been the target of nightly violence earlier this summer. The Portland Police Association is a labor union that represents members of the Portland Police Bureau.

A group of demonstrators broke into the building, set the fire and were adding to it when officers made the riot declaration just after 11:30 p.m., police said. Officers used flash bangs to force the protest away.