Graphic footage has emerged showing US police cursing at a man who had just been fatally wounded by an elderly deputy who accidentally fired his gun instead of his Taser.

Oklahoma man Eric Harris was shot from behind while fleeing from police in Tulsa on April 2.

Deputy Bob Bates, 73, allegedly meant to use his Taser to subdue Harris but instead fired a single round from his sidearm.

Officials have said the incident was an accident and would not be investigated unless the sheriff's office asked them to.

However, new video has now emerged showing how brutally police treated Harris after he was shot.

In the police body-cam video, Harris can be seen fleeing from officers down a street.

Police say he was running after he was caught trying to sell a 9mm pistol and ammunition to undercover officers, however, he was unarmed when shot.

After multiple warnings for Harris to stop and get on the ground, Mr Bates' voice can be heard yelling "Taser!"

A gunshot rings out and immediately Mr Bates can be heard again, saying, "I shot him, I'm sorry".

Harris falls to the ground and is held down by a number of officers.

"He shot me man, I'm losing my breath," Harris says.

"F--- your breath," one officer says.

"You shouldn't have f---ing ran," another yells.

The video shows police at first also refuse to believe that Harris was shot, however, authorities said as soon as they realised, they called in paramedics.

Harris died about an hour later in hospital.

The video is likely to inflame racial tensions in the US, where a recent spate of deaths of unarmed black men at the hands of white police officers has at times resulted in rioting and protests.