Demonstrators have set fire to a police station in Minneapolis on the third day of violent protests over the death of a black man who was pinned down by police.
Staff at the third precinct, the focus of many of the protests, were forced to evacuate as crowds forced their way into the building on Thursday night.
Rioting spread across the US city following the death of George Floyd, whose neck was kneeled on for almost eight minutes during his arrest on Monday.
In footage of Mr Floyd’s arrest recorded by a bystander, he could be heard pleading that he could not breathe until he slowly stopped talking and moving.
A police spokesman confirmed that staff had evacuated the station "in the interest of the safety of our personnel”.
Livestream video showed the protesters entering the building, where fire alarms blared and sprinklers ran as fires were set.
A state of emergency has been declared in Minnesota and the state’s governor Tim Walz called in the National Guard as the unrest escalated.
Four Minneapolis police officers were fired on Tuesday after the footage emerged.
Hours after the officers’ dismissals were announced, thousands of protesters filled the streets close to the scene where the incident took place.
Some stores in Minneapolis and the suburbs closed early on Thursday, fearing more rioting, as the city shut down its light-rail system over safety concerns.
The protests that began Wednesday night and extended into Thursday were more violent than Tuesday's, which included skirmishes between officers and protesters.
Mayor Jacob Frey appealed for calm. "Please, Minneapolis, we cannot let tragedy beget more tragedy," he said on Twitter.
Fire crews responded to about 30 intentionally set blazes during the protests, including at least 16 structure fires.
Multiple fire trucks were damaged by rocks and other projectiles, the fire department said. No one was hurt by the fires.
The US Attorney's Office and the FBI in Minneapolis said they were conducting "a robust criminal investigation" into Mr Floyd's death.
President Donald Trump has said he had asked an investigation to be expedited.
The FBI is also investigating whether Mr Floyd's civil rights were violated.
Derek Chauvin, the officer who kneeled on Mr Floyd's neck, was fired along with three other officers involved in the arrest.
The next day, the mayor called for Mr Chauvin to be criminally charged.