But Mayor Jenny Durkan has not said how or when authorities will remove the 500 or so demonstrators who have established a makeshift encampment behind barricades in the Capitol Hill district.

"It is unconstitutional and illegal to send the military into Seattle," said Durkan, a first-term Democrat, at a Thursday news conference. "There is no imminent threat of an invasion of Seattle."

Activists have occupied the area since police on Monday moved street barricades and abandoned their East Precinct station in a move city officials say aimed to reduce tension.

In a Youtube video, Seattle's police chief, Carmen Best, said it was not her decision to leave the precinct.

"You fought for days to protect it, I asked you stand on that line day in and day out to be pelted with projectiles, to be screamed at, threatened and in some cases hurt," Best told her department in the video.

Protesters used the police barricades to section off the area, calling it the "Capitol Hill Autonomous Zone".

"We're not going to let this happen in Seattle. If we have to go in, we're going to go in," Trump told Fox News on Thursday.

"Let the governor do it. He's got great National Guard troops ... But one way or the other, it's going to get done. These people are not going to occupy a major portion of a great city."

On Sunday, a man was arrested after driving his car into a crowd of protesters in the area that became the "autonomous zone" the following day.

He then shot and wounded a demonstrator who confronted him as he came to a stop, according to police and witness video.

Major US cities have been convulsed by marches, rallies and sometimes violence for more than two weeks over the death of a black man, 46-year-old George Floyd, while in Minneapolis police custody.

Australian Associated Press