An 11-year-old boy and his father have died after police shot the man at a sports oval on the Mornington Peninsula.
Commander Doug Fryer said four local police officers arrived at the oval on Frankston-Flinders Road in Tyabb on Wednesday evening shortly after having been called there by ambulance staff.
Police would not say if the father inflicted the boy's injuries. On Thursday morning they confirmed that the father died in hospital at 1.30am.
Police confirmed they shot the 54-year-old Chelsea Heights man in the chest after they were called to the oval on Frankston-Flinders Road after reports that a boy had sustained head injuries.
The boy was treated by paramedics at the scene but was unable to be revived. Polcie corrected earlier reports that the boy was 12.
A junior cricket team had just finished training at the time. Police arrived and were confronted with a man holding a knife.
They tried to talk him down but were unsuccessful. They then tried to subdue him with capsicum foam and later shot him once in the chest, Commander Fryer said.
"This was a dynamic, live critical incident. I won't comment on their exact conduct," he said.
He was treated by paramedics but died at the scene.
An Ambulance Victoria spokeswoman said paramedics had also treated a man in his 50s for chest injuries, and flew him to The Alfred hospital.
Commander Fryer said the boy's injuries were "significant" and "quite brutal". His father sustained life-threatening injuries.
He said police had already spoken to witnesses at the scene, including some children, and called for others who police believed had yet to come forward to call CrimeStoppers.
He would not comment on what else police saw at the scene, but said that the incident was "complicated" and involved other locations.
Commander Fryer said that Homicide Squad was now investigating the boy's death and that Professional Standards Command was looking into the police officers' conduct.
He also said that IBAC had also been called and would provide further oversight.
Commander Fryer said the boy's mother had been told of his death and was distraught: "The mother has been advised, she was in the vicinity at the time but I can't go into the details of what she saw."
"The death of a young child is always going to be horrific and I don't know how the mother's going to cope, she probably never will be able to."
Commander Fryer said the boy's father and mother were enstranged.
Police have cordoned off the oval, at Bunguyan Reserve in Tyabb, where a number of local sports clubs play, including the Tyabb Tennis Club and Tyabb Football Club.
Wayne Murray, who lives about 200 metres from the oval, said that junior cricket and football teams were playing on the oval when the police shooting happened.
"I was having tea, I walked out the back door about 30 seconds after I heard the police (drive in)...things had gone quiet and I went to turn around and you hear a pop-pop," he said.
"It was absolute chaos once the first ambulance rolled in, a lot of police came in and then the air ambulance came in and landed on the oval.
The oval was cleared shortly afterwards.
Local Taylor Le brun, 16, came to the oval after she learned of the incident from neighbours.
"It's unexpected so what could happen now? Because this has happened, what's next? You can't underestimate anyone now apparently."