The explosion of violence in Meadow Heights ended in police shooting and wounding a knife-wielding man.
A young police constable was also in hospital, recovering from stab wounds.
The suspect, in his 20s, is believed to be mentally ill and to have attacked his sister and mother.
Police say he then turned on a motorist, 60, who stopped to help, stabbing him several times in the back before fleeing back inside his Meadow Heights home.
He returned when police arrived and, despite being hit with capsicum spray, stabbed a constable who it's believed had only just graduated from the police academy.
The assailant was then shot twice in the chest by police officers.
The good Samaritan and his assailant were admitted to Royal Melbourne Hospital yesterday afternoon. The assailant was in a stable condition last night while the good Samaritan was in a critical condition.
A police spokeswoman said the offender remained under police guard and was yet to be interviewed.
"The initial advice we have is that the son has been agitated, and that he had an argument with his sister and his mum has intervened," Assistant Commissioner Tim Cartwright said.
"And it was at that stage the situation escalated. The mother and daughter were not stabbed - they were both choked - so their injuries are relatively minor".
The woman is understood to be in her 50s, while her daughter is in her 20s.
At least five ambulances were called to the scene, at the corner of Paringa Boulevard and Pascoe Vale Rd, just after 2.30pm.
Shocked neighbours watched as the injured were treated and rushed to hospital.
