Police have had a tough time controlling anti-racism protestors in the US city of Seatle.
The incident occurred in one of the most tensed of several rallies held across the country on Saturday.
Reports indicate that police officers used stun grenades and pepper spray, as protesters set a fire and broke windows of buildings. The march was in support of ongoing protests in Portland.
About forty-five protestors were arrested while 21 officers were reported to have sustained several degrees of injuries.
The demonstrations erupted following violent clashes in Portland between protesters and federal agents deployed by President Donald Trump despite opposition from local and state leaders.
Thousands of protesters had initially gathered peacefully in Seattle carrying signs such as “Feds go home” and “We are living in a police state”, and shouting chants of “No justice, no peace”.
A group then set fire to the construction site for a youth detention facility before smashing windows of a courthouse and nearby businesses, police said. Authorities said rocks, bottles, fireworks and mortars were thrown at officers, and one of them was taken to hospital with a leg injury.
Police, however, declared the demonstrations a riot and said they were investigating whether an explosive device was used against a police station.