Chicago Mayor Rahm Emanuel appealed for calm on Tuesday as the city prepared for possible protests in connection with the release of a video of the "chilling" shooting.

The footage shows police officer Jason Van Dyke fire at teenager Laquan McDonald on October 20, 2014. Prosecutors allege he shot the victim 16 times.

McDonald can be seen walking away from the officer before his body strikes the pavement as he is shot. He lifts his head, moves an arm and then at least one other gunshot appears to strike his chest.

The officer then walks into the shot and kicks a knife away from Mcdonald's hand.

Officer formally charged

Just a few hours before the highly-anticipated video was released, Van Dyke was charged with murder at Chicago's main criminal courthouse.

The 37-year-old was denied bail and If convicted, he could face 20 years to life in prison.

"To watch a 17-year-old young man die in such a violent manner is deeply disturbing and I have absolutely no doubt this video will tear at the hearts of all Chicagoans," Cook County prosecutor Anita Alvarez said at a news conference after the hearing.

The seven other responding officers did not believe deadly force was necessary, she added.

The footage is the latest in a string of police shootings caught on camera that have sparked mass protests over the use of deadly force by police against minorities.

The uproar has become an issue in the 2016 US presidential election campaign.

Rally turns violent

Meanwhile in Minneapolis, tensions remained high following Monday night's shooting during a demonstration over the killing of another black man, 24-year-old Jamar Clark.

Two people were arrested after several white men fired into a crowd of protesters from the Black Lives Matter movement. Five people were wounded, none seriously.

Police said Clark died in a struggle with police responding to a domestic disturbance on November 15.

mm/bw (AP, AFP, Reuters)