Police fired tear gas outside the White House as as anti-racism protesters again took to the streets of major US cities to voice fury at police brutality.
With the Trump administration branding instigators of six nights of rioting as domestic terrorists, there were more confrontations between protesters and police and fresh outbreaks of looting.
Violent clashes erupted repeatedly in a small park next to the White House, with authorities using tear gas, pepper spray and flash bang grenades to disperse crowds who lit several large fires and damaged property.
Washington's mayor ordered a curfew from 11pm until 6am, as a report in the New York Times said that President Donald Trump had been rushed by Secret Service agents into an underground bunker at the White House on Friday night during an earlier protest.
The shocking videotaped death on last Monday of an unarmed black man, George Floyd, at the hands of police in Minneapolis ignited the nationwide wave of outrage over law enforcement's repeated use of lethal force against unarmed African Americans.
The Department of Defence said that around 5,000 National Guard troops had been mobilised in 15 states as well as the capital Washington, with another 2,000 on standby.
"Congratulations to our National Guard for the great job they did immediately upon arriving in Minneapolis, Minnesota, last night," President Donald Trump tweeted, adding that they "should be used in other States before it is too late!"
The widespread resort to uniformed National Guards units is rare, and it evoked disturbing memories of the rioting in US cities in 1967 and 1968 in a turbulent time of protest over racial and economic disparities.
Trump blamed the extreme left for the violence, saying he planned to designate a group known as Antifa as a terrorist organisation.
Atlanta Mayor Keisha Lance Bottoms said Trump, who has often urged police to use tough tactics, was not helping matters.
"We are beyond a tipping point in this country, and his rhetoric only enflames that," she said on CBS.
Joe Biden, Trump's likely Democratic opponent in November's presidential election, visited the scene of one anti-racism protest.
"We are a nation in pain right now, but we must not allow this pain to destroy us," Biden tweeted, posting a picture of him speaking with an African-American family at the site where protesters had gathered in Delaware on Saturday. (AFP)