A man has been shot dead by police after allegedly severing his sister's arm during an attack, with the victim in a coma with life-threatening injuries.
Victoria Police Assistant Commissioner Russell Barrett said the altercation was reported to police by the pair's mother and took place at a home in Yarra Junction, 55km east of Melbourne, on Wednesday evening.
Police heard screaming coming from inside the home shortly after arriving at the scene.
"They then entered the bedroom and were confronted by a female who appeared to be unconscious and appeared to have a limb that was partially severed, being strangled by a man," Mr Barrett told reporters on Thursday.
Officers deployed their Tasers three times in an attempt to stop the assault, but the man continued to strangle his sister, Mr Barrett said.
An officer discharged their firearm, fatally shooting the man.
"This is tragic, it's every police officer's nightmare," Mr Barrett said.
"Both police officers are distressed. They understand the realities of their job ... but it's not what they come to work to do."
The woman was flown to the Royal Melbourne Hospital, where she remains in a coma with life-threatening injuries.
Mr Barrett said homicide detectives and forensic examiners remain at the scene, which he described as "graphic and dramatic".
He confirmed a sword was also found inside the home.
Premier Jacinta Allan described the shooting as distressing and said her thoughts were with the family.
"They're going to be deeply, deeply traumatised by this tragedy," she said.
The man is known to police through his medical condition.
State Coroner John Cain attended the scene on Wednesday night.
Homicide Squad detectives will investigate the matter with oversight from Professional Standards Command, as is standard procedure for a fatal police shooting.
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