Leyonhjelm defends controversial tweet

Crossbench senator David Leyonhjelm has defended using a deadly incident in Melbourne to make a statement about guns.

Four people are dead and at least 20 have been injured after a rogue car ploughed into pedestrians in Melbourne's Bourke St Mall on Friday afternoon.

Four children, including a three-week-old baby and two-year-old were among the injured. A mangled wreckage of a pram found at the scene, with a section of it coming to rest on the car.

The Liberal Democrat, an outspoken supporter of gun owner rights who favours easing restrictions on guns, has come under fire for using the incident to suggest it's people, not objects, that kill.

"Probably one of those semi-automatic assault cars," he tweeted as the disaster unfolded.

His comment has prompted hundreds of angry replies, with many calling on him to resign for making jokes about the disaster as families wait to find out if loved ones have been injured or killed.

Senator Leyonhjelm told AAP the outrage "only emanates from those who are too stupid to get it".

"My comment referred to the 'rogue' car, as if the driver is irrelevant," he told AAP.

"It's people who commit crimes, not inanimate objects.

"The same argument applies in the debate about firearms."

But his comment angered many, who took to twitter to criticise the senator.

Barrister and human rights activist Julian Burnside tweeted: "So ignorant, and in such bad taste. The tragedy is that Leyonhjelm is in our parliament. He disgraces our parliament and himself."

Former journalist and commentator Mike Carlton said: "Leyonhjelm is a grub. That is all."

Greens Leader Richard Di Natale has called on Senator Leyonhjelm to apologise.

"This is a tragedy and not the time for crass political point scoring," Senator Di Natale told AAP.

"Senator Leyonhjelm needs to pull his head in and apologise for his insensitive comments."