Hundreds of President Donald Trump's supporters staged a motorcade Monday near the protest-hit US city of Portland, where demonstrators, police and right-wing groups have clashed in months of anti-racism demonstrations.

Groups of armed men in paramilitary gear were among the crowd that included families and older people before some 300 vehicles drove through Oregon City, a Portland suburb.

Oregon's largest city has seen over 100 days of protest including one stand-off late last month, in which a far-right activist was shot dead and the man suspected in the killing was later fatally shot as police moved in to arrest him.

Organisers of the "Oregon For Trump 2020" motorcade, held on the US public holiday of Labor Day, said they would not try to enter the city itself in order to "keep it safe."

The parade was decked out with US flags, Trump banners and the occasional sign that read, "Keep America first".