A man identified as Dimitrious 'Jimmy' Gargasoulas allegedly drove a car through a crowd of pedestrians on Bourke Street, killing four people and injuring at least 30 others.
Among the four people killed were a 10-year-old girl, a 25-year-old man, a 33-year-old man and a 32-year-old woman. There are fears the death toll will rise.
A three-month-old baby girl who was rushed to hospital by police officers is among seven people with life-threatening injuries.
Three people are in a critical condition at the Royal Melbourne Hospital and three are in a critical condition at The Alfred.
A 32-year-old Indian woman who had been living in Australia with her husband and child is among those fighting for her life.
The mother, who works as an integration developer, is now in a critical condition at The Alfred with fractures to her neck and abdomen. The injuries are near her spinal cord.
Mr Gargasoulas, 26, is in hospital after being shot in the arm by police. He is expected to be charged on Saturday.
Mr Gargasoulas is accused of stabbing his brother, Angelo, in his mother's public housing flat in Windsor on Friday morning. Police said he has a history of family violence, as well as mental health and drug problems.
On Wednesday night, Mr Gargasoulas allegedly attacked 76-year-old Gavin Wilson, who lives at his mother's housing commission flats, and demanded the keys to his car.
Mr Gargasoulas tried to trash a St Kilda Bar after being denied entry to the venue the night before he allegedly went on the rampage.
The 26-year-old, who is a father to a number of children, had been posting angry comments on social media this week about God, war and police.
The Coroner has launched a forensic investigation into the incident as Victoria's controversial bail laws could be set for a shake-up.
Police said the incident was not terror-related.