All of the people involved in a fatal incident at a home in Melbourne’s south-east on Monday are related, Victoria Police Chief Commissioner Shane Patton says.

Investigators were called to a home on Springvalley Way at Narre Warren South about 1pm on Monday.

Police have not yet determined the exact circumstances of the incident but several family members were attacked.

Police are not looking for anyone else in connection with the incident.

A 42-year-old woman died in hospital and a 70-year-old woman and a three-year-old girl are in a serious condition in hospital.

A 15-year-old boy is under police guard in hospital and has not yet been questioned.

Police Commissioner Shane Patton has told Melbourne radio station 3AW all of those involved are related.

“It’s an absolute tragic incident out there,” he said.

“Obviously the homicide [squad] is conducting significant inquiries and forensic analysis at the scene, but it appears to involve family members.”

On Tuesday, a bouquet of flowers was laid outside the home.

Neighbour Heather Kunze said her husband comforted one of the family before police arrived. Photo: ABC

Karl and Heather Kunze live in the same street and Mr Kunze was working in his garden when the incident happened.

He said he was upset he could not help.

“I just saw ambulances everywhere out the front and the lady was sitting on the grass over there and I asked if she was all right,” he said.

“I’m shattered because, as I said to the police when they came here, if I had known I could have done more.

“It’s very devastating, I mean, to happen next door. I’ve never heard nothing from there. Maybe kids crying.

Ms Kunze, said the family was very quiet and the grandmother would take the kids off to school every day.

They had lived next door for 10 years.

“We were both upset, we both had a cry last night because it’s sad, it’s sad what has happened to that family,” she said.