
Heavily armed officers were deployed on the streets in the heart of the city, which is hosting the Australian Open tennis tournament.
"Paramedics are treating a number of people after they were hit by a car in Bourke Street," Ambulance Victoria said.
Victoria Police said the "exact circumstances of the events are still being determined".
"Pedestrian access has been closed along Bourke Street between Williams and Swanston. Police are asking for the public to avoid the area."