Expert evidence to start in Bourke St case

The first of four medical experts is expected to face intense questioning in court to determine the mental fitness of a man charged over Melbourne's deadly Bourke Street rampage.

A 12-person Victorian Supreme Court jury is on Wednesday scheduled to hear from a psychiatrist who will give his opinion on the health of Dimitrious "Jimmy" Gargasoulas to help jurors decide whether he's fit to stand trial.

The 28-year-old is charged with six counts of murder and 28 charges of attempted murder over the January 20, 2017 rampage through the city's pedestrian mall.

Gargasoulas' lawyer Theo Alexander told Tuesday's opening of the special hearing that he must establish his client is unfit to stand trial.

The court was told Gargasoulas has schizophrenia, a diagnosis agreed by both prosecution and defence experts.