Protesters hurled what police described as “projectiles” at officers during the demonstration that started late Tuesday night and stretched into Wednesday, the statement said.
Officers started to disperse the protesters after they refused to do so and used crowd control munitions that were not described in the statement, though tear gas was not used.
Portland has been gripped by nightly protests for nearly three months since the police killing of George Floyd in Minneapolis.
The demonstrations, often violent, have targeted police buildings and federal buildings. Some protesters have called for reductions in police budgets while the city’s mayor and some in the Black community have decried the violence, saying it’a counterproductive.
US President Donald Trump sent more than 100 federal agents from the US Department of Homeland Security to safeguard federal property — a move that instead reinvigorated the protests.