A car that allegedly swerved into fans outside a gaming convention, killing one man and leaving another fighting for life, continued driving for 120metres after impact in a detail of the investigation police have labelled 'extremely odd'. 

The grey Toyota is understood to have mounted a kerb where three men were standing outside the Supanova Comic Con and Gaming event at the Melbourne Showgrounds, just after 5pm on Saturday.

The car allegedly struck the trio who were on their way home from the event, with one dying at the scene, and another rushed to hospital with life-threatening injuries. Both are in their 20s.

Detective Inspector Craig McEvoy said a 33-year-old Werribee man, who was allegedly driving the vehicle, was arrested at the scene by an off-duty police officer.

'For unknown reasons the car has travelled across the southbound lanes, up on to the footpath where it has impacted two young males in their 20s, who were walking in a group of three,' he said.

'One of the males has (died) at the scene, the other has sustained significant lower limb injuries and has been conveyed to hospital.'

Supanova Comic Con & Gaming organisers released a statement, saying a minute's silence will be held as the two-day event continues at 10am on Sunday. 

Detective Inspector McEvoy said it was 'extremely odd' as the vehicle had 'travelled a significant distance along the footpath'.

'The car then travelled along the footpath approximately another 120metres where it has come to rest,' he said.

'The driver was then arrested by an off-duty police officer who was assisted by members of the public.'

Police are investigating what sparked the incident, including whether speed, alcohol or drugs were involved.

The driver remains under police guard in hospital.

A witness, Tom, was leaving the convention with his wife and daughter when they saw a Toyota allegedly speed past them on Langs Road.

'I heard a screech and a guy (allegedly) mounted the kerb at an erratic speed, hit a couple people,' Tom told The Age.

Tom said the car did a U-turn before driving back down the street.

The driver then stalled, according to the witness, who attempted to perform a citizen's arrest.

'I said, "You're not going anywhere, mate",' Tom said.

Victoria Police quickly arrived and arrested the driver.

Tom said his wife, who is a paramedic, worked on a victim who was allegedly hit by the car for 20 minutes before ambulances arrived.

'He couldn't move, but he was breathing,' Tom said.

Supanova is a convention about science fiction and fantasy TV shows, comic books, gaming and collectables. 

Police are urging anyone who witnessed the incident, has CCTV or dashcam vision or have any information, to contact Crime Stoppers.

The Supanova Comic Con and Gaming event posted a statement on Facebook, sharing its condolences to those impacted by the incident.

‘We here at Supanova Comic Con & Gaming are deeply saddened and distressed by the incident that occurred outside the Melbourne Showgrounds this evening,’ the statement read.

‘Our thoughts and prayers go out to all those affected by the unspeakable tragedy that has happened on our doorstep.’

The convention will continue as planned today.

‘Supanova will continue to support all Supa-Fans that come through our doors tomorrow morning, and we will be holding a minute’s silence in sympathy and solidarity of the affected families and friends at 10am before opening our doors to our event,' the statement said.