A good Samaritan who was stabbed repeatedly in the back when he came to the aid of two women in Melbourne’s north yesterday remains in a serious but stable condition in hospital this afternoon.

The 65-year-old man’s alleged attacker is also recovering in the Royal Melbourne Hospital from gunshot wounds, after he was shot by police during a violent domestic dispute in Meadow Heights.

Detectives have placed the man under police guard and are waiting to interview him when his condition improves.

Police were called to the Paringa Boulevard address about 2pm yesterday after reports of a domestic confrontation between a man and his mother and sister.

Assistant Police Commissioner Tim Cartwright said the mother, aged 59, had fled the house after her son had choked her and her daughter.

She ran from the family home pleading for help and the good Samaritan, who was walking by, went to her aid.

"At that stage he came out of the house armed with a knife and stabbed the passerby in the back several times," he said.

Police arrived at the scene and went to the the aid of the two victims. By then, the man had returned to the house but he rushed back out to confront police.

"They called on him to drop the knife, he has not complied, he confronted the members and they sprayed him and the spray had no effect," he said.

Assistant Commissioner Cartwright said the man then lunged at a police officer with a knife and cut him.

He was then shot several times in the upper body by another police officer.

"I don’t think there was any other option other than to shoot him at that stage," Assistant Commissioner Cartwright said.

He said it was "horrific" that a man who had gone to the aid of a victim was now in hospital as a victim himself.

"Here’s a man doing what we hoped people would do - helping an elderly woman in distress," he said.

The policeman was taken to hospital and treated for a deep cut to his right arm.

The mother and her 22-year-old daughter were also taken to hospital with minor injuries.

The policeman and the daughter have since been released, while the mother remains in the Northern Hospital.

Police were investigating whether the attacker, who earlier in the day had had a row with his sister, was suffering from any mental illness.

Neighbours said that they heard up to four shots fired during the dispute on the boulevard near the intersection of Pascoe Vale Road.

A pillow yesterday lay on the side of the street where neighbours had rushed to help the victims until ambulance crews arrived.

The police forensic team scoured the nearby pavement for clues, while homicide detectives were called in to assist in the investigation.

Assistant Commissioner Cartwright said it appeared that the confrontation had developed from a row into a far more serious situation.