Warning: This footage contains scenes that some people may find disturbing.

An investigation is underway into the death of an unarmed black man, who was shot by a Tennessee police officer.

The entire incident was shown live on Facebook.

Rodney James Hess was surrounded in Crocket County and asked to speak to "the higher commands," when two shots were fired through his windscreen before screams of pain ring out.

His family says the officer was unprovoked, but police maintain Mr Hess tried to strike them with his car twice before the live-stream began on Thursday.

Fiancée Johnisha Provost watched the stream from home and says her partner, who is bipolar, struggled in the moment.

"He couldn't get his mind together. That's why he asked for a higher command," she said.

"I always told him, 'Babe, if you are ever in a situation where you need help, ask the person in charge for the higher command to help you,' and that's what he kept saying," she told CNN.

Footage from the officer's dash and body cams have also been obtained to review and the District Attorney will determine whether the officer's behaviour was justified.

Newshub.