Police were reportedly heard chanting “whose streets, our streets” after making arrests during the third consecutive night of protests in St Louis, Missouri.

The protests were sparked by the acquittal of former St Louis police officer Jason Stockley in the fatal shooting of black man Anthony Lamar Smith.

David Carson, a reporter at the St Louis Post-Dispatch, said he had heard police chanting the slogan during Sunday night's clashes.

Footage of the incident appeared to confirm his and other reporters' accounts, though the video remains inconclusive.

Mr Carson said on Twitter: “I spoke with the commander at the scene, he said he did not hear the chant, but said chant was not acceptable, said he would deal with it.” St Louis police have been contacted for comment.

Hundreds have gathered every day since the "not guilty" verdict was announced following Mr Stockley's trial. While demonstrations have been fairly calm during the day, smaller groups that remain at night have broken windows, thrown objects and sprayed unknown chemicals at police officers.

Buses carrying police officers in full riot gear and shields arrived Sunday night, and some sustained injuries, although none were life-threatening, according to St Louis Police statements. Officers arrested more than 80 people on Sunday.

Police kettled tens of protesters in the early hours of Sunday morning before mass-arresting a number of those in the crowd. Among the arrests was local journalist Mike Faulk, who tweeted shortly before his arrest: We are closed in on all four sides... People freaking out".

St Louis police department has also come under fire after footage showed an elderly woman being pushed to the ground in a clash with police.

In the video, police with plastic shields can be seen advancing on the woman, ultimately pushing her to the ground. Several officers continue to move forward, stepping over her body, while others physically block protesters who appear to be trying to help her.

St Louis Police say an elderly woman who was knocked down by officers was disobeying orders, and has been charged with “interfering”.

The protests were sparked by the acquittal of former St Louis police officer Mr Stockley who said he was acting in self-defence when he shot Mr Lamar Smith.

State prosecutors claimed Mr Stockley had planted a revolver in Mr Smith’s car after his death to justify the killing, pointing out his DNA was discovered on the weapon, while Mr Smith’s was not.

They also cited internal police vehicle camera footage recorded shortly before the shooting, in which Mr Stockley can be heard saying to his partner, “We’re killing this motherf***er.”

In his ruling, Judge Timothy Wilson said the state failed to prove that Mr Stockley had not acted in self-defence.