A demonstration billed as a march for "law and order" in the streets of Portland, Oregon descended into chaos on Saturday night as rival political groups brawled in the centre of the city.

Members of the right-wing group Patriot Prayer and their left-wing adversaries, sometimes known as Antifa, clashed outside a popular bar on Southwest Washington Street.

The fight only ended when riot police rushed in and fired pepper balls at the brawlers.

"Patriot Prayer has had many rallies in Portland that attract white nationalists, neo-Nazis, Islamaphobes, xenophobes and homophobes," said the filmer, who identified himself only as John.

"Many of their events attract counter protesters and often turn violent," he added.

Patriot prayer has had many rallies in Portland that attract white nationalists, neonazis, islamaphobes, xenophobes and homophobes. Many of thier events attract counter protesters and often turn violent. This is just another one where violent proud boys get the excitement they were looking for.