Thousands of National Guard troops are now on patrol in major US cities after five consecutive nights of protests over racism and police brutality that boiled over into arson and looting.

President Donald Trump blamed anarchists and far-left activists for the violence, threatening to officially designate ANTIFA - the umbrella term for such groups - as terrorists.

Curfews failed to quell the bloody clashes that replaced peaceful daytime demonstrations over the death of a black man seen on video gasping for breath as a white Minneapolis police officer knelt on his neck.

George Floyd, 46, was filmed pleading: "I can't breathe." Derek Chauvin was later arrested and charged with third degree murder. Three other officers who were with him have been fired but for now, face no charges.

Political leaders today appealed to citizens to give constructive outlet to their rage without destroying their communities.

Lori Lightfoot, the mayor of Chicago, said her city was sharply limiting access to its central business district after violent protests. She reflected the exasperation of many officials and ordinary residents over the turn from peaceful protest to explosive violence.

She told CNN she was "hurt and angry at those who decided to try to hijack this moment and use it as an opportunity to wreak havoc, to loot and to destroy. You should be ashamed of yourselves. What you have done is to dishonour yourself, your family and our city."

The shocking videotaped death of Mr Floyd last Monday ignited a nationwide wave of outrage over law enforcement's repeated use of lethal force against unarmed African Americans.

Governor Tim Walz mobilized all of Minnesota's National Guard troops to help restore order. Police fired tear gas and stun grenades to clear streets of curfew violators last night in Minneapolis, and National Guard troops protected the state capitol in St. Paul.

Mr Walz extended the curfew for tonight and praised police and guardsmen for holding down violence, saying, "They did so in a professional manner. They did so without a single loss of life and minimal property damage."

"Congratulations to our National Guard for the great job they did immediately upon arriving in Minneapolis, Minnesota, last night," President Trump said in a tweet adding that they "should be used in other States before it is too late!"

A person loots a T-Mobile store near the White House in Washington DC

The US Department of Defense 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.

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.

Los Angeles, Chicago and Atlanta were among two dozen cities ordering people to stay indoors overnight but police and protesters still clashed in numerous cities.  

In Washington DC, protesters faced off with secret service agents outside the White House and 11 police officers were injured, a spokesman said, including one who suffered a fractured leg.

Multiple arrests were reported by US media in Minneapolis, Seattle and New York as rallies continued through the night. Officers in Los Angeles fired rubber bullets and swung batons during a testy standoff with demonstrators who set fire to a police car.

Several top officials from the Trump administration, including US Attorney General William Barr, have blamed ANTIFA and other "agitators" for taking over the protests.

A member of the National Guard patrols outside a burnt-out building in Minneaopolis

"The violence instigated and carried out by ANTIFA and other similar groups in connection with the rioting is domestic terrorism and will be treated accordingly," Mr Barr said following Mr Trump's tweet stating "the United States of America will be designating ANTIFA as a terrorist organisation".

It is not clear how many, if any, of the protesters participating in demonstrations are from ANTIFA, which experts note is not an organisation but rather an amorphous movement.

Atlanta Mayor Keisha Lance Bottoms said that President 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. "And he should just sometimes stop talking."

Melvin Carter, the African American mayor of St Paul - the capital of Minnesota and twin city of Minneapolis, the epicentre of the protests - told CNN: "There are some people in our streets who are driven there by a passion for our community.

"And then there's folks in our streets who are there to burn down our black-owned barbershops, to burn down our family-owned businesses, our immigrant-owned restaurants."

Democratic presidential candidate Joe Biden condemned the violence, but said US citizens had every right to demonstrate.

"Protesting such brutality is right and necessary," he said in a statement. "But burning down communities and needless destruction is not."

In Dublin, there were peaceful protests outside the US embassy and US ambassador's official residence in a show of solidarity following the death of George Floyd.

Read the latest analysis on the US unrest by Brian O'Donovan here.