Fireworks had reportedly been set off, which started the fire. Photo: Reuters.

A police station in Minneapolis has been set on fire after protesters calling for justice for George Floyd set off fireworks, according to reports. Dramatic images show the Minneapolis Police Department’s Third Precinct surrounded by flames on Thursday night, local time.

The station's windows were broken and protesters climbed over fences as officers retreated having fired projectiles, reports the New York Times.

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Images later showed officers abandoning the department as rioters celebrated, posing for pictures in front of the flames.

“This is 400 years of anger,” one protester, Justin Galbraith, told The Daily Beast.

Rioters were seen cheering as the building went up in flames. Photo: Reuters.

“There are so many innocent lives lost by the police. We protest peacefully and there is no accountability. So this happens,” demonstrator Cecilia Zwak said.

It comes as Minnesota's governor Tim Walz activated the National Guard to help police restore order against protests - now into their third night - over the death of unarmed black man Mr Floyd. Graphic video footage shows the 46-year-old gasping for breath as white officer Derek Chauvin kneels on his neck for several minutes before he loses consciousness.

Four city police officers involved in the incident, including Chauvin, were fired from their jobs the next day. The Floyd case is reminiscent of the 2014 killing of Eric Garner, an unarmed black man in New York City who died after being put in a banned police chokehold as he, too, was heard to mutter, "I can't breathe."

Protesters thronged Minneapolis streets for a third day on Thursday chanting "I can't breathe," as they rallied peacefully at the Hennepin County Government Center and marched through downtown, demanding the four officers be swiftly arrested.

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"There is probable cause right now" to make those arrests, civil rights activist the Rev. Al Sharpton said as he addressed the crowd.

"We're not asking for a favour. We're asking for what is right."

Garner's mother, Gwen Carr, said Floyd's case had renewed the trauma she suffered six years ago.

"This is just opening up an old wound, and pouring salt into it," she said.

Protesters gather outside the burning police station. Photo: Reuters.

At a morning news briefing, Police Chief Medaria Arradondo apologized to Floyd's family, conceding his department had contributed to a "deficit of hope" in Minnesota's largest city.

Hours later, officials overseeing investigations from the U.S. Justice Department, FBI, Minnesota Bureau of Criminal Apprehension and local prosecutors appealed for calm at a joint news conference, as they gathered evidence.

"Give us the time to do this right, and we will bring you justice," County Attorney Mike Freeman told reporters.

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Floyd, a Houston native known affectionately to friends as "Big Floyd" and who had worked as a nightclub security staffer, was reportedly suspected of trying to pass counterfeit money when police took him into custody.

A protester spays graffiti on a police car.

Wednesday's disturbances, punctuated by looting, vandalism and arson, began hours after Mayor Jacob Frey urged local prosecutors to file criminal charges in the case.

Most protesters had been peaceful, while a smaller, core contingent engaged in unruly behaviour, the police chief said.

Sympathy protests erupted on Wednesday in Los Angeles and Thursday in Denver, with hundreds of demonstrators blocking freeway traffic in both cities.

George Floyd died after being restrained by police.

In a sign the Floyd case had garnered international attention, the United Nations High Commissioner for Human Rights Michelle Bachelet urged U.S. authorities on Thursday to deal with "entrenched and pervasive racial discrimination" in America's criminal justice system.

Police department records posted online show 18 internal affairs complaints filed against Chauvin, 16 of which were closed without discipline. The veteran officer allegedly tried to kill another black man, Ira Latrell Toles, during a domestic violence call in 2008.