A man has reportedly been gunned down by police after a car crashed and burst into flames on Bourke Street Mall.
Three people have been injured, according to Ambulance Victoria, while the man is in a critical condition and under police guard.
Bystanders spotted a car on fire on Bourke Street Mall, between Swanston and Russell Streets, outside the Target store.
Users on social media have reported hearing an "explosion", while vision of the incident has suggested a man attacked police with a knife, before seemingly being shot by an officer.
VISION (WARNING: GRAPHIC):
"Police initially responded to a report of a car on fire near the corner of Swanston Street about 4.20pm," Victoria Police wrote in a statement.
"A man was arrested at the scene and has been taken to hospital under police guard in a critical condition. Police are not looking for anyone further at this early stage. A small number of people are being treated for stab wounds.
"The exact circumstances are yet to be determined at this stage. The area has been cordoned off and the public are urged to avoid the area.
"Anyone with information or who witnessed the incident is asked to go to Melbourne West Police Station to make a statement. We will provide further information when it comes to hand."
Victorian premier Daniel Andrews posted an update on the situation himself, urging people to "please avoid the area and always follow the instructions of emergency services personnel".