A "heroic" off-duty police officer has undergone surgery after arresting a man who allegedly mowed down more than a dozen people in a Melbourne car rampage.
The anonymous officer was the first on the scene and was injured fighting with the 32-year-old driver who had crashed into a tram station.
The off-duty sergeant's bravery potentially saved more people from being injured as uniformed officers made their way to the scene.
"That's putting service above self. You don't know what you're walking into when you walk into a situation like that, in Melbourne," Police Association Victoria secretary Wayne Gatt said.
"The member and his family are still in a difficult period.
"Our members take an oath to look after the community. That doesn't stop when we're off duty. And they do that quite proudly and we're quite proud of them when they do."
He said 16 of the officers who responded to the attack on Thursday afternoon were on their first day on the job.
"Imagine that, your first day in Victoria Police after training, being confronted with that carnage."
The driver was arrested after allegedly driving into pedestrians on busy Flinders Street, leaving 18 people in hospital.
Fourteen people were still in hospital on Friday morning, with three, including a man in his 80s, in a critical condition.
The off-duty officer is recovering in hospital after surgery and is in a stable condition.
He has been lavished with praise from police and Victorian Premier Daniel Andrews.
Victoria Police Acting Chief Commissioner Shane Patton said the "heroic" officer was having surgery on Friday morning for an injured finger.
"To step in when you see trauma ... not understanding what the threat is ... it is heroic," he said.
"[It was a] great response, great actions with everyone who responded at the time, including all the police and emergency services."
Victorian Premier Daniel Andrews last night said it "would be right to single [the officer] out for special praise".
"He instinctively came to the aid of others, in the protection of public order, and potentially, avoiding so much other carnage," Mr Andrews said.
