Police have fired tear gas and issued warnings for crowds to disperse as a curfew starts for a second night in Ferguson in the US state of Missouri,

It is in force from midnight (05:00 GMT) to 05:00 (10:00 GMT).

Police wearing body armour and gas masks said "aggressors" in a crowd of several hundred protesters were advancing on a police command post.

The suburb of St Louis has been tense for more than week, since police shot dead a black teenager, Michael Brown.

US Attorney General Eric Holder has ordered a federal post-mortem on the body of Michael Brown, 18, to take place "as soon as possible".

A preliminary private autopsy report found that Mr Brown was shot at least six times, including twice in the head, the New York Times reports.

The bullets did not appear to have been shot from very close range due to the lack of gunpowder on the victim's body, forensic pathologist Michael Baden was quoted by the paper as saying.

He flew to Missouri on Sunday to conduct a separate autopsy at the request of the family.

The Quick Trip is the convenience store on a petrol station forecourt in Ferguson, wrecked in violence a week ago.

They call it the Ground Zero of the unrest in Ferguson.

Parked there after 21:00 on Sunday evening, we could see clouds rise up behind it as police began to disperse the protests on West Florissant Avenue, with a helicopter beaming down a spotlight.

We could also hear the sirens of the acoustic weapons used to clear people out.

When "flash-bangs" exploded on the forecourt, a bit like a ground-level firework display, designed to move people on, we drove down a side street as the crowd ran towards us.

Several of them were spluttering and pouring bottles of water into their eyes as they felt the effects of tear gas.

We saw one young woman collapse to the floor as she struggled to breathe, although she recovered some time later.

Protesters around me at an intersection on the edge of the neighbourhood are asking why the police dispersed what they say was a peaceful protest, more than two hours before the scheduled curfew.

(BBC)