A six-year-old girl has died in hospital after a stabbing that claimed the life of a woman in Melbourne's north.
The young girl and a 39-year-old woman, believe to be her mum, were both found with critical injuries at a home in Mill Park at about 7.50pm on Thursday.
The woman died at the scene while the girl was rushed to hospital, where she later died.
Detective Inspector Dean Thomas said a 40-year-old man injured himself while speaking with police and is in a critical condition in hospital under police guard.
"A 10-year-old girl managed to escape and flee. She was not physically injured," he said, adding that she is speaking with police.
"It's very difficult for her. She's been through an absolutely terrible, traumatic incident ... we want to make sure she's as good as she can be."
Police believe the woman ran to a neighbours home, pursued by the attacker, to call for help. Neighbours alerted emergency services.
They understand the man is the woman's husband, and the father of the two girls.
He said reports emergency services had been called to the property just before 1pm on Thursday would form part of their investigation.
"We believe that a person at the address was assessed at that point in time and emergency services cleared," he said.
He said they're awaiting further medical advice but expect that the man may survive his injuries. He will be interviewed in the coming days if medically cleared.
Just over an hour later, two people were found with critical injuries at a Mordialloc, after gunshots were heard.
The men, aged 62 and 72, later died.
Police believe their deaths are the result of a dispute between neighbours in a block of units.
A 73-year-old man was arrested by police after pointing a gun at officers.
Det Insp Thomas said officers fired a shot at the older man. He was not hit and retreated into a home, before surrendering to officers a short time later.
He will be interviewed on Friday.
"It's not often that we will get two jobs overnight, two homicide jobs, and we have a total of four people killed," he said of the night's events.
"To get them on the same night like that doesn't happen all that often, so our thoughts are very much with the families of these people and also the friends that are impacted by it."
Police are appealing for witnesses or anyone with dash cam footage from the Mill Park or Mordialloc areas, but have stressed they're not looking for anyone else in relation to both incidents.
Meanwhile, a man was also found dead after a house fire at Endeavour Hills in Melbourne's outer southeast earlier on Thursday evening.
The death and fire is also being probed by police.
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