Police have released CCTV showing the moment a black teenager appears to draw a gun before he is shot dead by a white officer in a killing that sparked more violent protests in Missouri.

Antonio Martin, 18, was killed at a petrol station in the St Louis suburb of Berkeley on Tuesday night.

Authorities said the officer was responding to a shop-lifting call at around 11.15pm when he saw two men and approached them.

CCTV video appears to show one of the men drawing and pointing a handgun at the officer.

St Louis County Police Chief Jon Belmar said the officer stumbled backwards and fired three shots, one of which struck the teenager.

Martin was dead when paramedics arrived, the chief said.

Detectives said they recovered Martin's 9mm pistol at the scene.

Following the shooting, a crowd of up to 300 people gathered around the cordoned off forecourt.

A wall of police officers, some wearing riot helmets, guarded the scene with bystanders shouting at them in a tense standoff.

Footage showed fireworks being let off and some officers were injured after bricks were thrown.

On Wednesday, Berkeley's mayor attempted to ease tensions by distancing the shooting from the killing of Michael Brown Jr in nearby Ferguson, in August.

"This is not the same as Ferguson," Theodore Hoskins said.

"There is this jump to conclusion that all policemen are guilty. Jumping to conclusion before investigation is not acceptable."

He added: "Some people die because the policeman initiates it. Some people die because they initiate it.

"At this point, our review indicates that the police did not initiate this."

Chief Belmar said he understood the emotions of the community but that "bad choices were made" by the victim.

"This individual could have complied with the officer, he could have run away, he could have dropped the gun.

"All sorts of things could have happened. It didn't have to end with him approaching the officer with a 9mm pistol in his hand," he said.

Martin's mother, Toni Martin, was at the scene overnight. She was heard crying "that's my baby" when she found out her son was dead.

She told the St Louis Post-Dispatch that Martin had been out with his girlfriend, adding: "His girlfriend told me the police was messing with him. He was trying to get up and run and they started shooting."

Ms Martin said he was a "good young man" who was "trying to get his life back together" after being expelled from school.

She claimed her son was not carrying a gun.

Chief Belmar said the victim was known to police and had previously been arrested for assault and armed robbery.

Berkeley is the neighbouring suburb to Ferguson where police officer Darren Wilson shot dead Mr Brown on 9 August.

Protests spilled over into violence when a grand jury decided not to charge Mr Wilson.

Demonstrations in cities across the country gained momentum when a New York grand jury decided not to charge police over the death of Eric Garner, a 43-year-old black man who police put in a chokehold.

About 200 people marched in New York on Tuesday, defying Mayor Bill de Blasio's call for protests to be suspended after two police officers were killed in their patrol car on Saturday in an apparent revenge attack.

Michele Jawando, a legal expert at the Center for American Progress, told Sky News the protests are the result of a "broken trust" in many communities.

"Underlying all of the angst is this sense that black lives - and this is a phrase that we've heard - or certain communities of colour, when it comes to policing in their neighbourhood, there is this broken trust between law enforcement and the communities that they often police," she said.

"Finding a solution to create trust between law enforcement and the communities that they serve is a goal that we can all agree upon."