Far-right demonstrators and “antifa” protesters clashed in Oregon over the weekend, resulting in multiple injuries and arrests, authorities said.

The chaos broke out when at least three rival groups — including members of the #HimToo movement, the right-wing hate group “Proud Boys” and anti-fascist organizations — collided in Portland on Saturday during competing rallies that had been planned in different parts of the city.

Police in riot gear had to step in to break up the melees. They arrested three people on assault and harassment charges.

Eight people, including three police officers, were treated by medics at the scene, the Portland Police Bureau said. Three people were taken to local hospitals after they were attacked, cops said.

Among those injured was, an editor of the right-wing website Quillette, Andy Ngo, who said he was attacked by antifa protesters. Ngo said the protesters swiped his camera equipment and that he had to be treated for injuries to his face and head at a hospital.

Police said they received reports of milkshake cups filled with quick-drying cement being thrown at people. Pepper spray was also used by cops and demonstrators.

Protesters also turned on cops — launching water bottles and eggs at officers.

As skirmishes continued, cops declared the situation a civil disturbance and warned that any participants in the protests faced being arrested for unlawful assembly.

“There are hundreds of peaceful free speech events in the city in a given year that do not result in violence,” Assistant Chief Chris Davis said in a statement.

“Unfortunately, today some community members and officers were injured. We are actively investigating these incidents to hold those responsible accountable.”

With Post wires