Gabriel Messo, 31, attacked his 54-year-old mother Lilla at the John Coutts Reserve in Gladstone Park about 3.30pm on Thursday.

The Gladstone Park man was shot dead by junior officers at the scene and the woman is now in Royal Melbourne Hospital in a critical condition.

Media outlets named the mother and son on Friday, with police only confirming that they were known to each other.

State coroner Judge John Cain went to the site of the fatal shooting and will investigate the incident, it was confirmed on Friday.

The police patrol arrived at the parkland on Katrina Drive following reports of a man assaulting a woman and witnessed the horrific attack, Victoria Police Assistant Commissioner Luke Cornelius said.

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

Police were initially unable to identify the woman because of the extent of her injuries.

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

Police appealed to witnesses of what's believed to have been a stabbing attack.

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

Australian Associated Press