And police arrested a man known to the girls, who was at the Longmuir Road house at Watsonia, in the city’s north-east.

He was last night being questioned at Heidelberg police station.

Detectives did not reveal the man’s relationship to the girls, but confirmed he was known to them.

Police would also not reveal how the children died or whether they had any visible injuries.

Police arrived at the house at 2.40pm and found both girls.

Paramedics arrived soon after but their CPR attempts failed.

“They administered CPR for some time but were unable to save the patients,” an Ambulance Victoria spokesman said.

Police assistant commissioner Andrew Crisp said an Easter family get-together had ended in tragedy.

“It’s a time for families to get together and enjoy each other’s company, and this will have a significant impact on friends, on family,” he said.

“I’ve heard today that several of our police members have been in tears.”

The girls’ deaths shocked the neighbourhood, with Rachel Fish, who lives a few doors away saying: “This has had always been a quiet area for families.

“The wildest thing that’s happened here is the odd teenage party.”

One man, who said his name was Mark, said he had been best man at the wedding of the children’s parents. Mark said the couple had split up more than a year ago.

He said the girls’ father still lived in a granny flat behind his former mother-in-law’s house.

He did not know where the girls’ mother was.

“No one can get in touch with her at the moment,” he said.

A couple said they had heard sirens, gone outside to investigate and found the street flooded with police and paramedics.

“This is just terrible,” “David” said.

He and his wife said an elderly woman lived in the house and feared it was her grandchildren who had died.

“It’s really sad if that’s the case,” said David’s wife.

“She’s a lovely lady. I thought she lived alone.”

Another neighbour, Ben Cameron, said he has often seen the girls playing in the area.

“I’ve seen those kids. I know the family. It’s pretty frightening and scary,” he said.

Longmuir Road was blocked last night with forensic police still searching the house.