A person was shot dead Saturday in Portland following clashes between Black Lives Matter protesters and supporters of US President Donald Trump, police said.

The Oregon city has been an epicenter of BLM protests since the police killing of unarmed black man George Floyd in Minnesota in late May, and according to local media a "caravan of hundreds of cars" of Trump supporters also converged there on Saturday.

Portland Police tweeted a political rally was "caravanning throughout downtown Portland," adding: "There have been some instances of violence between demonstrators and counterdemonstrators. Officers have intervened and in some cases made arrests."

OregonLive reported "clashes" and "tense moments" between the groups, although police did not say whether the shooting was related to the demonstrations.

The shooting occurred at around 8:45pm downtown, police said later in a statement, adding a homicide investigation was under way.

"Portland Police officers heard sounds of gunfire from the area of Southeast 3rd Avenue and Southwest Alder Street," the statement said.

"They responded and located a victim with a gunshot wound to the chest."