Seattle protests: Nurse hit with pepper spray while trying to help man pushed over by police

'I've seen footage from Hong Kong of how you have to get people away from the cops because once they get them, they arrest them, they brutalise them, they beat them'

Law enforcement shot a stream of what appeared to be pepper spray directly into a nurse's face as she tried to help someone who had been pushed over by police in Seattle amid fresh protests against police brutality.

Police declared a riot in the Washington city, as demonstrations continue across the US in the wake of police killings of black Americans with a renewed outrage over Donald Trump's deployment of federal agents into American cities.

Video posted to social media shows the nurse, wearing her green scrubs, walking along a grass verge as police march towards protesters. As a man is knocked over by heavily-armoured officers she rushes forward and kneels down to help him, but is immediately sprayed in the face. She falls backward but then is able to stand up and is helped to safety by an onlooker.

The nurse, whose identity was not immediately known, later told Simone Del Rosario of TV channel Q13 Fox she was trying to "pull the guy away". She said: "I've seen footage from Hong Kong of how you have to get people away from the cops because once they get them, they arrest them, they brutalise them, they beat them.

"I saw the guy with the baton and the guy that had the tear gas launcher, I guess, and it's like – OK you're aiming that at people, you're muzzle-sweeping people in the crowd with that?"

Earlier this month The Independent's chief US correspondent, Andrew Buncombe, was arrested by police while covering a protest in Seattle. Despite repeatedly identifying himself as a journalist he was held at a police station for more than six hours, forced to wear prison overalls, manacles and a waist chain, assaulted and threatened with a charge of failure to disperse.

On Saturday police fired tear gas, pepper balls and blast balls into crowds of hundreds in Seattle's Capitol Hill neighbourhood, days after the Trump administration sent tactical units into the city.

At least 45 people were arrested, and police said "21 officers sustained injuries" though most returned to duty. One officer was hospitalised for a knee injury, police said in a statement.

Seattle's Wall of Moms, inspired by a Portland group joining protesters to defend against police attacks, said the group marched peacefully until police and "unmarked Federal Contractors tear gassed a bunch of moms, allies and youth".

"In broad daylight," the group said. "With no provocation from peaceful media or marchers. All Moms (and allies) know we can do better than this."

Department of Homeland Security forces have terrorised protesters in Portland, Oregon, demonstrators say, and police declared Saturday's protests in that city a riot after a group compromised fencing around a federal courthouse used to stage federal officers. Legal experts have questioned their presence there.

The president has ordered a "surge" of federal officers into American cities as he embraces a "law and order" agenda imposing strict, violent control over protests that have gripped the nation over the last two months.

Seattle Mayor Jenny Durkan said that the president's threats to send federal forces into Seattle "exacerbate the situation on the ground, endanger communities, and jeopardize the work of local officials".

"The president unilaterally deploying paramilitary-type forces into American cities should concern all Americans," she said. "His blatant disregard for the constitution – and for the safety and well-being of our residents — is textbook despotism.”

Police declared a riot after a small group broke off from the demonstration and entered a construction site near a juvenile detention centre and "set fire to portable trailers and other equipment, and broke out windows on personal vehicles in the area and court facilities", according to a police statement.

Outside the Seattle Police Department's East Precinct, several people "began spray painting and attempting to disable security cameras and a fence perimeter around the precinct", police said.

The precinct has been the site of nightly demonstrations, including a nearly month-long occupation of the building.

Earlier on Saturday, a federal judge issued a temporary restraining order blocking the Seattle City Council's ordinance banning police use of crowd weapons like pepper spray, rubber bullets and blast balls.

In a statement on Thursday, Seattle Police Chief Carmen Best said that the City Council's measure effectively "eliminates these tools as available less-lethal options across the board."

"The Council legislation gives officers no ability to safely intercede to preserve property in the midst of a large, violent crowd," she said. Allowing this behaviour deeply troubles me, but I am duty-bound to follow the Council legislation once it is in effect."

An "autonomous zone" established by protesters within several blocks inside Seattle's Capitol Hill neighbourhood had experimented with a community-governed space without law enforcement, relying on co-ops and a street festival atmosphere, while the president declared it a "domestic terror" threat. Police eventually cleared the area earlier this month following several shootings in the area.

In a statement on social media before the weekend's demonstrations, Washington Governor Jay Inslee said the president has "sent federal officers to Seattle because he is itching for a confrontation. He wants attention."

"We shouldn't give him either," the governor said. "Keep it peaceful, keep the attention where it belongs – on building a better, more just Washington for everyone."