Homicide Squad detectives were investigating an attack on an elderly woman who was found fatally injured at a house in Coleraine, about 35km from Hamilton, in Victoria's southwest.
Local officers found the 81-year-old woman alive shortly after 1am on Saturday, but she died at the scene.
Police arrested and interviewed an 81-year-old Coleraine man who was known to the victim before charging him with murder on Saturday evening.
He has been remanded in custody and will face the Warrnambool Magistrates Court on Monday.
In a separate incident, two men were also stabbed at a house gathering in Sydney's west overnight, one of them suffering critical wounds.
Emergency crews were called to a residential unit in Patricia Street, Mays Hill, in the city's inner west, in the early hours of Saturday following reports a man in his 20s had sustained serious injuries.
He was located and treated at the scene by paramedics for an apparent life-threatening knife wound to the torso before being taken to Westmead Hospital.
Police said a second man of similar age was found nearby with a wound to his arm. He was also transported to Westmead.
It is understood the pair and others at the address were known to each other.
The Coleraine incident comes days after an Australia-first knife ban targeting young offenders.
Victorian parents were urged on Thursday to hand in their children's machetes and knives at police amnesty posts.
A total of 45 stations across the state will host disposal bins set up for the three-month initiative.
Carrying one of the deadly, long and broad-bladed knives is outlawed, while a sales ban with some exemptions is already operating.
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