North Carolina's governor has declared a state of emergency in the city of Charlotte, after violence erupted during a second night of protests over the police killing of a black man.
Keith Lamont Scott was shot dead by a black officer on Tuesday.
One protester remains in a critical condition after a "civilian on civilian" shooting, police said.
Mr Scott was the third black man killed by US police in a week. Such shootings have sparked nationwide protests.
Riot police in Charlotte used tear gas as they faced hundreds of protesters. The local police department said four officers were injured.
Earlier North Carolina Governor Pat McCrory said he had "initiated efforts" to deploy the national guard and highway patrol to help deal with the protests.
"Any violence directed toward our citizens or police officers or destruction of property should not be tolerated," he said.
The demonstrators are angry that Mr Scott, 43, was killed by police on Tuesday afternoon at a block of flats in disputed circumstances.
Police were serving an arrest warrant on another person when they say they saw Mr Scott get out of a car with a handgun.
Officers say he was repeatedly told to drop his handgun before he was shot but his family say he was reading a book, as he waited for his son to be dropped off by the school bus.
Dash-cam footage of the incident will be viewed by Charlotte's mayor but not released to the public "at that time", the city said.
It is legal to openly carry a handgun in North Carolina, but a special permit is required to carry a concealed weapon.