The family of the African-American man whose death has triggered days of unrest in Charlotte, North Carolina, released a dramatic video of the police shooting on Friday, raising pressure on the authorities to make their own footage public.

The police have refused to release body-cam and dash-cam video of the shooting Tuesday, which they say shows Keith Lamont Scott posed officers a threat.

His death is the latest in a string of police-involved killings of black men that have fueled outrage across America.

Charlotte has been rocked by three nights of violence-marred protests, prompting the governor to declare a state of emergency in the southern US city.

Hundreds of protesters were out again on Friday night calling for the release of the videos amid a greater presence of National Guard troops, but the atmosphere was calmer than during previous days.

A curfew beginning at midnight (0400 GMT) is in effect for a second night after protesters defied the order on Thursday.

Hundreds of demonstrators were also marching in the southern city of Atlanta in a protest calling for police reform organized by the NAACP, the black community's main civil rights organization.

Charlotte's case has also touched the US presidential race, with Democrat Hillary Clinton's campaign announcing her plan to visit the city on Sunday before postponing it to a week later after Charlotte Mayor Jennifer Roberts asked both major candidates to delay visits, citing "very stretched resources for security."

Clinton weighed in about the video issue earlier Friday, tweeting that police should release its footage "without delay."

President Barack Obama called for understanding as he celebrated the opening of the Smithsonian's African American museum in Washington this weekend.

The museum "allows all of us as Americans to put our current circumstances in a historical context," the first black US president said.

- The video -
Scott was shot and killed during a parking lot encounter with police searching for another person wanted for arrest.

The police say he had a handgun. His family says he was holding a book.

The two minutes and 16 seconds of smartphone footage filmed by Rakeyia Scott, released by her lawyers to AFP and other news media, does not show the shooting itself -- and does not conclusively answer the question of whether he was armed -- but captures the moments surrounding it as she pleads with officers not to open fire.

"Don't shoot him, he has no weapon! He has no weapon! Don't shoot him!" she is heard saying.

"He has a TBI, he's not going to do anything to you guys," she says, presumably referring to a traumatic brain injury. Neighbors have told AFP the 43-year-old Scott was disabled and had a stutter.

As she records, police are heard yelling "Drop the gun! Drop the gun!"

"Don't let them break the windows. Come on out the car," she shouts to her husband.

Four quick gunshots are heard, at which point the phone is pointing away from the shooting.

Moments later, the video shows Scott lying face down on the asphalt surrounded by officers.

"Did you shoot him? Did you shoot him?" Rakeyia Scott screams.

- The police stance -
Scott's family has viewed the police footage and are leading calls for it to be made public.

Charlotte Mayor Jennifer Roberts told reporters Friday she believes the video should be released -- but that doing so too soon could interfere with the probe by leading witnesses to change their accounts.

The police, too, say premature release of the video might interfere with a parallel state investigation.

"If I were to put it out indiscriminately and it doesn't give you good context, it can inflame the situation," Charlotte police chief Kerr Putney argued.

The footage does not provide "absolute definitive visual evidence that would confirm that a person is pointing a gun," he said earlier, but does indicate the officer was justified in shooting Scott.

"The officer perceived his failure to comply with commands, failure to drop the weapon and facing the officers as an imminent threat," Putney told Fox News.

- Contrast to Tulsa -
Charlotte's handling of the case contrasts sharply with a similar police shooting last Friday involving an African-American man in Tulsa, Oklahoma.

There, the video has been released and the white officer involved charged with first degree manslaughter.

In Charlotte, the officer identified as having shot Scott, Brentley Vinson, is black.

No gun is visible in the police video, which shows Scott stepping backward when he was shot, according to a family lawyer.

"His hands are down by his side. He is acting calm," the lawyer, Justin Bamberg, told CNN. "You do see something in his hand, but it's impossible to make out from the video what it is."