Vic security boosted after London terror

Police will bolster security at major events across Melbourne after a terrorist attack in London put them on a heightened alert.

Victorian Chief Commissioner Graham Ashton says "security overlays" and extra police are planned in case of copycat attacks.

"Last night's events just heightened it for us," Mr Ashton told 3AW on Thursday.

"We've got five footy games, the grand prix on this weekend and a bunch of other events.

"Particularly tonight we kick the (AFL) season off so there will be extra police down there (at the MCG) tonight."

Mr Ashton said police had also planned to prevent a possible "mixed motor attack" during the grand prix.

"Mixed motor attack is the preferred one at the moment and these things tend to trend," he told reporters.

A knife-wielding man ploughed a car into pedestrians on London's Westminster Bridge on Wednesday before fatally stabbing a police officer inside the gates of the country's parliament.

Four people were killed, including the assailant, and 40 others were injured.