Police officers react at the scene of a looting at the Dellwood Market after protests against the shooting of Michael Brown turned violent near Ferguson, Missouri. Reuters

The governor of the US state of Missouri has signed an order to send the National Guard to the town of Ferguson as protests over the police shooting of an unarmed black teenager continue.

Governor Jay Nixon said the decision came to "help restore peace and order and to protect the citizens of Ferguson".

Police in Ferguson said that they were attacked with molotov cocktails and bottles by protesters in the St Louis suburb and had "no alternative" but to respond.

Cpt Ron Johnson said that the attacks came just before a five-hour curfew came into effect at midnight local time.

"For those who would claim that the curfew was what led to [the] violence, I will remind you this incident began three and a half hours before the curfew was to have started," he said.

Ferguson Missouri St Louis
Tear gas rises from the ground after having been fired upon protesters who are continuing to react to the shooting of Michael Brown, in Ferguson, Missouri. Reuters

The unrest began after the killing of black teenager Michael Brown by a white policement in a street on 9 August. His shooting has stirred racial tensions in the majority-black suburb.

According to the New York Times, a preliminary private autopsy report found that the teenager had been shot at least six times, twice in the head.

However, an autopsy by the St Louis County Medical Examiner's office revealed that the teenager had been shot but did not disclose the number of times.

A federal autopsy, the third on Brown's body, is set to take place at the request of US Attorney General Eric Holder.

Forensic pathologist Michael Baden was quoted by the New York Times as claiming that the bullets were not shot from close range because of the lack of gunpowder on Brown's body when he was killed.