Police hunt for Vic murdered man's brother

Police believe the older brother of a man viciously murdered with a long blade at a Melbourne shopping centre may be heading interstate.

David Dick, 36, died after being slashed in the head with a long-edged blade as he stepped out of a car park lift at Westfield Doncaster shopping centre at 6am last Friday.

Police are urging Mr Dick's brother, Jonathan Dick, 39, to hand himself in to help them with their inquiries.

They believe he may be driving a blue or white sedan or station wagon and could be heading to NSW or Queensland.

Police have warned people not to approach him and said he had mental health issues but had chosen not to take medication.

They are concerned for his safety due to the "overwhelming situation".

"Don't do anything to hurt yourself, you just reach out to us and we'll make sure someone gets to you," Detective Inspector Michael Hughes said on Wednesday.

Jonathan has no criminal record, police say.

His uncle reported him missing since February 6, three days after his brother was attacked.