AT least four children have been injured after a car ploughed through pedestrians in Melbourne's CBD, with a pram dragged under a vehicle and left mangled in the road.
Witnesses said a baby was thrown from the pram and a three or four-year-old child may have been dragged up to 100 metres down the street, Sky News reported.
Christine Nixon, former police commissioner of Victoria Police, was on the scene a minute after the incident just before 1.40pm. She said a mother repeatedly begged her, "Where is my baby?" She responded, 'I don't know.'
Nixon also helped direct traffic afterwards.
The Royal Children's Hospital confirmed four children were being treated after the horrific incident at Bourke St Mall that left three dead and at least 20 injured, and the city centre in lockdown.
A man dressed only in red underwear has been arrested at the Elizabeth Street end of the mall and Ambulance Victoria is treating at least 20 people. The mangled wreckage of a pram is at a pedestrian crossing in front of the County Court on William St.
"There was a car that just sped along the footpath and hit people," a witness told police at the scene.
A Victoria Police spokeswoman said at this early stage they believe the man driving the car struck a number of pedestrians in the vicinity of Bourke and Queen Streets just before 2pm on Friday.
"Emergency services are assisting multiple patients but at least one person has been confirmed deceased," the police statement said.
"Pedestrian access has been closed on Bourke Street between William and Swanston streets." There were unconfirmed reports of shots being fired before the man was arrested. "There's someone on the middle of the ground and there's blood all over the street," Rishi Hathiramani, a CBD shopkeeper, told AAP. "I've seen accidents but never this bad.
"It's pretty brutal."
A number of CBD businesses are in lockdown, while others have been evacuated. "A heap of people ran into my store, it was horrible. Half of my staff are in tears," said a Strandbags manager.