Police have arrested a man in Melbourne after a car mounted a kerb and drove into pedestrians, killing one.

A grey Toyota struck two pedestrians on Langs Road in the Ascot Vale suburb just before 17:00 local time (07:00 GMT) on Saturday, Victoria Police said.

One pedestrian died at the scene and the second was taken to hospital with life-threatening injuries.

Police said the circumstances surrounding the collision had not yet been established and the arrested man was due to be interviewed.

Local media reported the crash happened outside the Melbourne Showgrounds, which had been hosting the two-day Supanova Comic Con & Gaming event.

Pictures of the scene showed a police cordon around the vehicle which appeared to have visible damage.

Det Insp Craig McEvoy told 9News that the driver had been arrested by an off-duty officer who received assistance from the public.

He said it was unclear whether the incident was intentional, but police would be investigating all avenues, including whether drugs or alcohol were involved.

The Sydney Morning Herald reported an eyewitness, Tom, said he "heard a screech and a guy mounted the kerb at an erratic speed, hit a couple people".

He said the car U-turned back down the street towards him before it stalled, and he claimed to have stopped the driver from fleeing.

Thousands of people had reportedly been expected to attend the event, which describes itself as the "home of Australia's pop culture fandom".

Celebrities including Lord of the Rings actor Andy Serkis and Harry Potter actress Bonnie Wright were announced as guests at the expo.