A woman is fighting for life after a frenzied attack which left her with injuries so severe that police were unable to identify her.

The woman was allegedly attacked by a man in his 30s at the John Coutts Reserve in Gladstone Park about 3.30pm on Thursday.

The man was shot dead by a patrol of junior officers that Victoria Police Assistant Commissioner Luke Cornelius said were shaken up by the incident.

The patrol arrived at the parkland on Katrina Drive following reports of a man assaulting a woman, and witnessed the horrific attack.

Mr Cornelius told reporters the officers tried to stop the man but had to make one of the worst possible decisions they could confront in their careers.

The woman was hospitalised in a critical condition and police weren’t able to identify her because of the extent of her injuries.

It is believed the man and the woman were known to each other and they might be family members, Mr Cornelius said.

The man does not have a criminal record but is known to police, who had recent contact with him.

“Nothing in that contact that indicated to us the events of today might have occurred,” he said on Thursday.

Police appealed to witnesses of the attack, believed to be a stabbing.

Homicide squad detectives will investigate, with oversight from Professional Services Command because a police firearm was discharged.

-AAP