Protesters outside Ferguson Police Department early Thursday 12 March

Two police officers in the flashpoint US town of Ferguson were shot early Thursday during a new protest over the treatment of blacks by the mainly white police force, an officer said.

One officer was shot in the face and the other in the shoulder as a protest rally outside the police station in the Missouri town was dispersing, St. Louis County police chief Jon Belmar told reporters. He said the officers were conscious but that their injuries were serious.

Ferguson in recent months has been one of the hot spots for the long-standing US problem of harsh treatment of young black men by mainly white police.

Earlier in the day, the Ferguson police chief resigned over a scathing US Justice Department report into the fatal shooting of unarmed black teenager Michael Brown by one of his officers back in August.

Ferguson police in riot gear

Brown was shot and killed by white police officer Darren Wilson, igniting angry protests and a national debate about race and law enforcement in America.

Wilson was not charged in that death.

Belmar said the protest that formed Wednesday night was dispersing when at least three shots were fired.

“The police officers were standing there and they were shot. Just because they were police officers,” Belmar told reporters at the scene of the incident, adding that the officers were alive and conscious.

Witness Markus Roehrer told CNN that the atmosphere at the protest was tense and that when he first heard the gunfire he thought it might be firecrackers.

“When I saw the cops go down, I said this is far worse,” he told CNN.

CNN broadcast blurry amateur video in which gunshots are heard, protesters run away in panic. A moaning voice is heard, then police are seen crouching down with weapons drawn.

Belmar said it was not really clear where the shooting came from.

But Roehrer said the sound came from some distance behind the small group of protesters, which he estimated at about 40 when the gunfire rang out.

“To put this on the protesters would be totally unfair,” he told CNN.