Protesters have clashed with police in the US state of Missouri after a black teenager, reportedly brandishing a gun, was shot dead by a white officer.

A crowd of around 300 people gathered near a petrol station in Berkeley on Wednesday, after the shooting death of 18-year-old Antonio Martin.

Protesters threw bricks and fireworks, two of which were directed at 50 officers at the scene, St Louis County police chief Jon Belmar said.

Martin was shot dead on Tuesday after reportedly pointing a gun at a police officer conducting a routine check at a petrol station.

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According to authorities, the policeman pulled out his own gun, stepped back, stumbled, and fired three shots. One of the bullets struck Martin, who paramedics declared dead at the scene.

Theodore Hoskins, Berkeley's mayor, attempted to diffuse tensions saying there were clear differences with Wednesday's case and that of Michael Brown, who was shot six times by a white officer.

"You could not even compare this with Ferguson," Hoskins said.

Berkeley is a few kilometres from Ferguson, where weeks of protests and riots erupted after a police officer shot the unarmed Brown in August.

Protests have flared across the US following a court decision not to indict Darren Wilson, the police officer who shot Brown.

Demonstrations gained in momentum after a New York grand jury decided not to charge the police officer over the death of Eric Garner, a 43-year-old black man who died in July when police tackled him and put him in a choke hold.

Source: Al Jazeera and agencies