Dramatic bodycam footage has emerged showing a man armed with a knife charging at a Minnesota cop before being fatally shot by the officer.

Steve Mattson screamed warnings before firing at Ronald Davis on September 15 in the Midway neighbourhood of St. Paul, Minnesota, after the 31-year-old ran at him with a blade.

The video, which was released by the St Paul's police department on Tuesday, shows Mattson shooting Davis dead after telling him to 'put down the knife,' which he ignored.

On Sunday, before police released the footage, protesters carrying 'Black Lives Matter' marched from the Saint Paul Western District to the location Davis died.

Ronald Davis (pictured) can be seen lunging towards the officer (left image) with a knife in his right hand. The officer draws for his weapon (right) and takes aim after asking him to put the weapon down repeatedly

Ronald Davis, pictured, can be seen attacking at officer Steve Mattson with a knife on the 15 September. He was then shot dead by the policeman. The 31-year-old attacker had a daughter and a wife

St Paul's police chief, Todd Axtell, said that the officer responded appropriately as he had to defend himself. Ronald Davis (pictured) attacked the officer with a knife after rear-ending him in St Paul, Minnesota

Yet, since the publication of the attack, anti police brutality activists have not been satisfied that Mattson's actions were justified.

They said it is not clear if the police could have used non-lethal force to subdue Davis.

They asked for the rest of the bodycam footage and the investigative materials to be released.

The video starts with Mattson exiting his vehicle when Davis can be seen running towards him. Davis had rammed into the back end of the officer's car.

Though he moved out of the way, Ronald Davis is shown to keep coming for the officer armed with a knife and what was later confirmed as a flashlight

Protesters said that it wasn't clear from the video whether the police officer could have used non-lethal force to subdue the assailant. They have asked to see the entirety of the footage

The 31-year-old appears to be carrying items in his hands which the police later confirmed were a flashlight and a knife.

As he moves out of the way of Davis's frenzied attack, the officer tries to shout at him to drop the weapon but he ignores him. Mattson then shoots Davis.

St. Paul's Chief of Police, Todd Axtell, supported the officer, saying he had no other option other than to defend himself.

Mattson can clearly be heard on the video asking the attacker to 'drop the knife' and to 'get away' before he is shot.

After he shoots Davis, Mattson calls for back up and says that the suspect is 'still at gun point' and for the handler to get a medical response to the scene.

Activists can be seen carrying posters of Davis and Black Lives Matter during a protest on Sunday through Saint Paul, Minnesota. Protesters say it isn't clear whether Mattson could have used non-lethal force to subdue the suspect