Three children are dead, a fourth is seriously ill and an injured woman is under police guard after the car she was driving crashed into a Melbourne lake.
Despite frantic efforts from passers-by and emergency crews, one of the four children, all believed to be under six years old, died at the lake.
A second child died on the way to hospital and a third died in hospital.
Witnesses say the car was travelling along Manor Lakes Boulevard at Wyndham Vale when it went over a footpath and drove across about 20 metres of parkland and shrubs before ploughing into the lake.
Police say the exact circumstances are yet to be determined, but a female driver and four children were in the car when it went into the water on Wednesday afternoon.
Nearby residents, passers-by and police jumped into the lake and tried to pull them from the submerged car.
But despite attempts to resuscitate the children, one died at the scene and two others died not long afterwards.
The surviving child is described as being in a serious condition, in the Royal Children's Hospital.
"The woman has been taken to hospital and is under police guard," police said.
The woman is in a stable condition in the Royal Melbourne Hospital.
Superintendent Stuart Bateson said it was too early to tell whether she was the mother of any of the four children.
"What we do know is that when the car left the road passers-by and police members got some of the children out and did CPR," he told reporters at the scene.
"What we do know is that we have a very tragic set of circumstances here and it is going to be a very harrowing investigation."
Everyone there had been affected, he said.
"When you come to a scene like this and my members in particular, who have been performing CPR for an extended period of time, are really feeling it."
Sara Omar, 17, was walking in the parklands near the lake's edge when the crash occurred.
"I didn't really see much because I was around the other side, but I heard a massive 'boom'," Ms Omar told AAP.
She saw a man run into the lake to retrieve the children.
"He broke the window of the back seat of the car and he tried to take the little kids out and he put them on the end of the lake," Ms Omar said.
"I saw the ambulance taking a little kid and I think they were resuscitating him."
One woman who lives opposite the lake saw firefighters pull one child from the vehicle.
"They couldn't get the car open," she told The Age.
"They were banging, trying to get the car open and trying to smash its windows."
Emergency workers tried CPR for a long time, she said.
"They looked very emotional, they were exhausted."
Police and emergency workers late on Wednesday had floodlit the area and placed a wide cordon around the vehicle.
Only the roof and upper portion of the windows of the dark-coloured vehicle is visible above the water line.
It will be pulled from water on Thursday, a Victoria Police spokeswoman told AAP.
People have begun to leave flowers at the lake.
