SEATTLE (REUTERS) - Thousands of people marched in Seattle on Saturday in the largest Black Lives Matter demonstration in weeks, with a renewed energy sparked by violent clashes between activists and federal agents in nearby Portland, Oregon.

Police said officers used non-lethal weapons in attempts to disperse the crowd in the late afternoon after some protesters set fire to the construction site for a King County juvenile detention facility and courthouse.

Seattle Police said on Twitter they were working to secure access for the city's fire department to the blaze, which it said was started by about a dozen people who were part of a large group of demonstrators.

By 8pm local time, a standoff continued as the police said 25 people had been arrested in the city in Washington state in the northwest of the United States.

One officer was hospitalised with a leg injury caused by an explosive.

US President Donald Trump said on Thursday that he expanded the deployment of federal police to Seattle, enraging local officials and igniting anger among protesters.

"We saw what was happening in Portland and we wanted to make sure in our city we were standing in solidarity with other moms," said Lhorna Murray, who attended on behalf of the newly formed Wall of Moms Seattle, replicating a tactic from the Portland protests where mothers dressed in yellow form a human wall between protesters and law enforcement.

The heavy-handed tactics of federal officers in Portland have drawn the ire of local leaders and Democrats in Congress, who say those officers are using excessive force and complain of overreach by the Trump administration.

US Attorney for the Western District of Washington Brian Moran said in a statement on Friday that federal agents are stationed in Seattle to protect federal properties and the work done in those buildings.

The Trump administration has also sent federal police to Chicago, Kansas City and Albuquerque over the objections of those mayors.

In Texas, one person was killed when several shots were fired amid a Black Lives Matter protest in downtown Austin on Saturday, authorities said.

Footage posted during a Facebook Live showed the moment when several shots rang out in the Texas capital as about 100 people marched and chanted, "Fists up! Fight back!"

Austin police and emergency medical services said on Twitter that one person was killed during the shooting. There were no other deaths or people shot.

Initial reports suggest that the suspect was carrying a rifle and had shot at the victim from inside a car. Police said the suspect has been detained.

Protests against racism and police brutality were sparked worldwide following the May killing of African-American George Floyd, who died in police custody in Minneapolis.

Floyd died after a police officer knelt on his neck for nearly nine minutes while detaining him.