A protester raises a fist near a fire during a demonstration outside the White House over the death of George Floyd at the hands of Minneapolis Police in Washington DC on Sunday. Photo: AFP

Police fired tear gas outside the White House late Sunday as major US cities were put under curfew to suppress rioting as anti-racism protestors again took to the streets 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 protestors 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.

Local US leaders appealed to citizens to give constructive outlet to their rage over the death of an unarmed black man in Minneapolis, while night-time curfews were imposed in cities including Washington, Los Angeles and Houston.

One closely watched protest was outside the state capitol in Minneapolis' twin city of St. Paul, where several thousand people gathered before marching down a highway.

"We have black sons, black brothers, black friends, we don't want them to die. We are tired of this happening, this generation is not having it, we are tired of oppression," said Muna Abdi, a 31-year-old African-American woman who joined the protest.

"I want to make sure he stays alive," she added in reference to her son, aged three. 

Hundreds of police and National Guard troops were deployed ahead of the protest.

At one point, some of the protestors who had reached a bridge were forced to scramble for cover when a truck drove at speed after having apparently breached a barricade.

The driver was later taken to hospital after the protestors hauled him from the vehicle, although there were no immediate reports of other casualties.

There were other large-scale protests in cities including New York and Miami.

Washington's mayor ordered a curfew from 11 pm until 6 am, as a report in the New York Times said that US 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.

Large-scale violence has rocked many US cities in recent days, and looters ransacked stores in a neighborhood of Philadelphia on Sunday.

In the Los Angeles suburb of Santa Monica, looting was reported at stores in a popular beachside shopping center.

Officials in LA - a city scarred by the 1992 riots over the police beating of Rodney King, an African-American man - imposed a curfew from 4 pm Sunday until dawn.

The shocking videotaped death on May 25 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.

AFP