While an increasing number of police departments have the cameras, the rules governing their use can be unclear.
A US police officer has shot a black man at a housing complex in Charlotte, authorities in North Carolina say, prompting street protests late into the night.
The Charlotte-Mecklenburg Police Department (CMPD) said on Twitter on Tuesday that demonstrators were destroying marked police vehicles and that approximately 12 officers had been injured.
Witnesses contradicted police reports that the man killed was armed, saying that he was unarmed and disabled, according to reports.
The man “has been named as Keith Lamont Scott”, said Al Jazeera’s Alan Fisher, reporting from Greensboro, North Carolina.
He said at least one protester was also injured in the protests.
The police officer was named as Brentley Vinson. Associated Press news agency said Vinson is black.
Television coverage showed police firing tear gas to break up the crowd protesting against police brutality.
“It is tense. There are still people on the streets,” our correspondent said.
Police killings of black men over the past few months have seen anger swell as many fear civil rights are being eroded.
According to a tally being kept by the Guardian newspaper, police have killed at least 193 black men so far this year. In all of 2015, police killed at least 306 black men.
The protests came only hours after another demonstration in Tulsa, Oklahoma, over the shooting there of an unarmed black man by police.
Charlotte police went to the complex about 4pm looking for a suspect with an outstanding warrant when they saw the man – not the suspect they were looking for – inside a car, police said.
Officers saw the man get out of the car with a gun and then get back in, police said. When officers approached, the man exited the car with the gun again.
At that point, officers deemed the man a threat and at least one fired a weapon.
Scott, the victim, was taken to Carolinas Medical Center and pronounced dead.
Officer Vinson, who shot Scott, has been placed on administrative leave, which is standard procedure in such cases. Vinson has been with the department for two years.
Detectives recovered a firearm at the scene and were interviewing witnesses.
Police blocked access to the area, which is about a mile from the campus of the University of North Carolina at Charlotte, as protesters gathered after the shooting.
Video from WCCB-TV in Charlotte showed police in riot gear stretched across a two-lane road confronting protesters at the apartment complex later in the night.
— Sarah Blake Morgan (@StorytellerSBM) September 20, 2016
Some of the officers flanked the main line on one side of the road.
Some protesters were heard yelling “Black lives matter,” and “Hands up, don’t shoot!” One person held up a sign saying “Stop Killing Us.”
In Tulsa, hundreds of people rallied outside police headquarters calling for the firing of police officer Betty Shelby, who shot Terence Crutcher, 40, on Friday in a confrontation that was captured on police dashboard camera and helicopter video.
Shelby’s lawyer has said that Crutcher was not following the officers’ commands and that Shelby was concerned because he kept reaching for his pocket as if he was carrying a weapon.
A lawyer representing Crutcher’s family says Crutcher committed no crime and gave officers no reason to shoot him.