Melbourne police are seeking information about a man wearing a clown mask who was seen waving a gun at pedestrians early on Tuesday morning.

Four people have so far come forward to say they were threatened by the man, who was seen leaning out of a car passenger window as the vehicle slowed to a crawl when passing victims across the St Albans and Sydenham area.

The clown stepped out of the car on one occasion but no-one was hurt during the bizarre 30-minute spree, though Sgt Mark Guthrie of the Brimbank Crime Investigation Unit said victims were in shock.

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"All the witnesses have described a weapon being pointed at them, a firearm, whether it is fake or not we do not know," Sgt Guthrie said.

"All the incidents happened within half an hour and within 10 to 15km of each other. It was half-hour of madness but why they did it, I can't put my finger on it.

"It was very scary for those involved, they all want them caught or for it to stop," he added.

Sgt Guthrie said the man had been described as wearing a full white face mask with red hair, red lips and red nose, riding in a white car that may have had other passengers.

"Each incident only last a few seconds before the victim was able to flee, so no one got a really good look at the offenders," he added.

"We also don't have a numberplate, so I would be really interested to hear from anyone else who may have been a victim or saw a car acting erratically in the area or anyone who may have any information about the matter."