A four-year-old girl thrown off Melbourne's West Gate Bridge this morning has died in hospital.
A Royal Children's Hospital spokeswoman said the girl died at 1.35pm.
A 35-year-old Hawthorn man has been charged with her murder and will appear in Melbourne Magistrates Court this afternoon.
The girl was flown to hospital after being rescued from the river beneath the bridge about 9.15am.
Homicide squad Detective Inspector Steve Clark said the alleged murder occurred at 9.10am - peak travel time - on the city-bound side of the bridge, close to the top.
It took place so quickly "no one had the opportunity to intervene", he said.
"He's got straight out of the car and taken the young girl and walked to the edge of the bridge, so that would have happened in a matter of seconds," Detective Inspector Clark said.
"Fortunately, the water police were here within 10 minutes so she was given medical attention fairly quickly.
"It's a dreadful set of circumstances and often you think you've seen it all and you haven't."
A man believed to be the father of the girl was arrested outside the Commonwealth Law Courts building at the corner of La Trobe and William streets about 10.30am.
A caller to Radio 3AW said he saw four or five police officers, including one with his gun drawn, surround a man on the ground outside the court building.
It is understood he had gone with his two other children to the building, which houses the Family, Federal and Federal Magistrates courts.
Police and paramedics were called to the courts building after staff noticed the man's "distressed state".
'Had enough'
A member of the court's staff said the man was crying and looked like "he'd had enough".
He had two other children, aged 6 and 8, with him and witnesses said he begged security guards to "take my kids".
One of the witnesses said the man was shaking uncontrollably and looked like he was "about to have a nervous breakdown".
The man was seen to approach court security guards and ask them: "Can you take my kids for me?"
About half-an-hour later, the couple saw the arrival of a woman they believed to be the mother of the two boys, who subsequently took them away.
Another witness saw four police officers, two of them holding evidence bags, lead the handcuffed man to a waiting divisional van.
Shaking violently
The man, who she described as balding, was "shaking violently".
A court source said a case involving the family was heard in the Federal Magistrates Court this week, when it is believed an agreement was reached on shared custody of the children.
A white Toyota Land Cruiser, believed to be owned by the man, was parked outside the court building this morning.
Children's toys and clothing could be seen in the back of the vehicle. It is understood it has been seized by police and will be analysed by investigators.
Witnesses have told police a man driving in the inbound lane of the West Gate Freeway pulled up near the top of the bridge and threw the child into the water below.
The girl was pulled from the water close to the western bank of the river on the northern side of the bridge about 9.15am.
50 minutes
Paramedics spent about 50 minutes resuscitating her before she was taken to hospital.
Ambulance Victoria paramedic team manager Trevor Weston, who was involved in the rescue, said it had not been easy.
"Anything that involves children takes its toll on paramedics," he said.
"Fortunately it's not a very regular occurrence but when it does [happen] it really does hit home."
Mr Weston said it was not clear how long the little girl, who he said had mainly internal injuries, had been in the water.
Detective Inspector Clark urged witnesses to phone Crime Stoppers on 1800 333 000.
- with Kate Hagan, Andrea Petrie and Erdem Koch.
* Support is available for anyone who may be distressed by calling SANE Helpline 1800 18 7263; Lifeline 131 114; Salvo Crisis Line - 9331 2000; beyondblue 1300 22 46 36.