FERGUSON (REUTERS) - Two police officers were shot during a protest outside the Ferguson, Missouri police headquarters early on Thursday, the police said, just hours after the city's police chief quit following a damning justice report into his department.

St. Louis County police chief Jon Belmar told reporters that a 41-year-old officer from his department was struck in the shoulder and a 32-year-old officer from the nearby Webster Groves Police Department was hit in the face around midnight as the crowd was starting to break up.

He said he did not know the conditions of the officers, whom he did not identify, but said they were both conscious and being treated at a local hospital. "These police officers were standing there and they were shot, just because they were police officers," Mr Belmar said.

The St Louis County Police Department Twitter account had earlier said both of the shot officers were from their department.

At least three shots rang out as the crowd protesting at the station was breaking up, Mr Belmar said. A few dozen demonstrators fled following the sound of gunfire around midnight with some screaming, "They hit a cop," according to a Reuters photographer at the scene.

Several dozen protesters had gathered in front of the Ferguson police department earlier on Wednesday night, just hours after the city's police chief Thomas Jackson announced his resignation.

The demonstration was largely peaceful, but later on some two dozen officers clad in riot gear faced off against the protesters, who had relocated to the street. At least two people were taken into custody at the time.

Mr Belmar said that the shooter was "embedded" in the group of demonstrators who were standing across from the officers at the time.

Prominent activist Deray McKesson said on Twitter that he was at the scene, adding that the gunfire did not appear to come from the group of demonstrators. "The shooter was not with the protesters. The shooter was atop the hill. We can live in a world without guns," Mr McKesson said.

Protesters had called for Mr Jackson's removal since the fatal shooting of unarmed black teenager Michael Brown by white Ferguson police officer Darren Wilson on Aug 9, 2014. The killing triggered nationwide protests and drew scrutiny to police use of deadly force, especially against black men.

Neither a grand jury nor the federal probe led to charges against Wilson.

Mr Jackson's departure was the latest in a string of officials who stepped down following a scathing report from the United States Justice Department that found widespread racially biased abuses in the city's police department and municipal court.

Wednesday's demonstration had been tense but peaceful throughout the night. Several dozen people attended, and at one point demonstrators hung a flag with the words "Racism Lives Here" over a silhouette of the St. Louis skyline and drew chalk outlines in the parking lot of the department.

Later, some two dozen officers clad in riot gear faced off against the demonstrators, who had relocated to the street. At least two people were taken into custody.