North Carolina Governor Pat McCrory has declared a state of emergency in the city of Charlotte, as violent protests continue over the police killing of African-American Keith Lamont Scott.

Violence erupted for a second night after Keith Lamont Scott was shot dead by a black officer on September 20.

One protester is in a critical condition after a “civilian on civilian” shooting, the city said.

Keith Lamont Scott was the third black man killed by police in a week. Such shootings have sparked huge protests recently.

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Riot police in Charlotte used tear gas as they faced hundreds of protesters. The local police department said four officers were injured.

The North Carolina governor 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,” Pat McCrory said.

The protesters are angry that 43-year-old Keith Lamont Scott was killed by police at a block of flats in disputed circumstances.

Police were serving an arrest warrant on another person when they say they saw Keith Lamont Scott get out of a car with a handgun.

Officers say Keith Lamont Scott 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.

Gov. Pat McCrory declared the state of emergency as rioters clashed with police, breaking windows and setting small fires.

The second night of protests had begun peacefully but the demonstration was interrupted by gunfire and a man in the crowd was injured.

The city initially said the man had been killed but then issued a clarification.

Demonstrators then threw bottles and fireworks at the officers, who were lined up in riot gear. Police fired flash grenades and tear gas to repel the crowds.

Several journalists were also reportedly attacked. A reporter and cameraman for Charlotte’s WCNC-TV were taken to hospital and a CNN journalist was tackled on live TV, local media report.

Police in Charlotte defended their actions in the death of Keith Lamont Scott by insisting he had been repeatedly warned to drop his gun.

Charlotte-Mecklenburg Police Chief Kerr Putney told a news conference Keith Lamont Scott first got out of the car with a gun, then got back into his vehicle when officers told him to drop his weapon.

He was shot when he emerged from his car holding his weapon. The police chief was unable to say if Keith Lamont Scott had been pointing his weapon at officers.

After her father’s death, Keith Lamont Scott’s daughter posted a video on Facebook in which she said her father had been unarmed and reading a book.

Kerr Putney said no book was found.

Charlotte Mayor Jennifer Roberts voiced her shock at the violent protests, which saw 16 police officers injured on September 20.