At least five US police officers were shot and wounded during violent protests over the death of a black man in police custody, the police and media said.
This is coming hours after President Donald Trump vowed to deploy the military if unrest did not stop.
Trump deepened outrage on Monday by posing at a church across from the White House clutching a Bible after law enforcement officers used teargas and rubber bullets to clear protesters.
The US Secret Service, charged with protecting the president, on Tuesday closed down until further notice the streets around the White House, media reports said.
Demonstrators set fire to a strip mall in Los Angeles, looted stores in New York City and clashed with police in St Louis, Missouri, where four officers were taken to hospital with non-life-threatening injuries.
An emotional St. Louis police commissioner, John Hayden, said about 200 protesters were looting and hurling fireworks and rocks at officers.
Hayden said: “They had officers with gas poured on them. What is going on?
“How can this be? Mr Floyd was killed somewhere else and they are tearing up cities all across the country.
“A police officer was shot during protests in Las Vegas. Another officer was ‘involved in a shooting’ in the same area.
“Officers were injured in clashes elsewhere, including one who was in critical condition after being hit by a car in the Bronx.”
Trump, a Republican, has condemned the killing of George Floyd, a 46-year-old African American who died after a white policeman pinned his neck under a knee for nearly nine minutes in Minneapolis on May 25, and has promised justice.
But with marches and rallies for racial equality and against police brutality having turned violent late each day in the last week, he said rightful protests could not be drowned out by an “angry mob.”
Trump said: “If a city or state refuses to take the actions that are necessary to defend the life and property of their residents, then I will deploy the U.S. military and quickly solve the problem for them.”
Floyd’s death has reignited simmering racial tensions in a politically divided country that has been hit hard by the coronavirus pandemic, with African Americans accounting for a disproportionately high number of cases.
Democratic Illinois Governor J.B. Pritzker on Tuesday urged patience, saying Americans could work through these tough issues.
He pledged to take legal action if Trump carried out his military threat.
“We can bring down the temperature, but not when the president … is standing up calling for troops, and law and order, and domination,” he told MSNBC. “We will fight him, and we will take it to federal court.”
Washington, D.C., Mayor Muriel Bowser, in a separate MSNBC interview on Tuesday, said there were no signs of active duty US military in the city overnight.
After his address, Trump posed for pictures with his daughter, Ivanka, and US Attorney General William Barr at St. John’s Episcopal Church near the White House.
The presiding bishop of the Episcopal Church diocese in Washington D. C., Michael Curry, was among those who criticized Trump’s use of the historic church for a photo opportunity.
“In so doing, he used a church building and the Holy Bible for partisan political purposes,” he said on Twitter. The church suffered minor fire damage during protests on Sunday night.
On Tuesday, Trump was scheduled to visit the Saint John Paul II National Shrine in Washington.