More tear gas fired at crowd in Missouri

US police have again fired tear gas to break up a crowd of demonstrators in the Missouri town of Ferguson, where a black teenager was shot and killed by a white police officer nine days ago.

Police in riot gear, supported by an armoured SWAT vehicle and a helicopter overhead, repeatedly ordered the crowd to disperse.

They then let lose with a volley of tear gas just after 11pm on Monday (1400 Tuesday AEST), sending the crowd - smaller than the one that clashed with police on Sunday - scurrying.

The standoff occurred near the residential street where 18-year-old Michael Brown was fatally shot by a local police officer in this St Louis suburb and after the release of a video which shows the scene immediately after the incident.

Local woman Piaget Crenshaw began filming shortly after Michael Brown was shot by police. Her video shows officers standing near the prone body of the 18-year-old man.

"God bless his soul" Ms Crenshaw can be heard saying. "Police just shot this boy right outside my apartment. They killed him."

The video was released as the results of a private autopsy were made public. They concluded that Brown was shot at six times – four times in the arms and twice in the head.

The shots came from in front of Mr Brown, the autopsy concluded.

His body will be the subject of a second autopsy by the US Department of Justice.

His death has triggered daily protests and nightly clashes with law enforcement officials, and prompted the deployment earlier on Monday of National Guard reservists.