Following several fatal attacks in the heart of Melbourne, including the deaths of six people in 2017, officers have been reminded they must take action to prevent members of the public being killed or badly hurt in a vehicle attack.

A new Victoria Police "hostile vehicle" policy gives them the green light to ram an offending vehicle, use roadblocks, box in the vehicle or shoot the offender as a last resort.

Police were criticised for not taking any action despite following James Gargasoulas's erratic driving for several hours before he drove his car down Bourke Street in January 2017, killing six people and injuring 27 others.

Deputy commissioner Shane Patton said while police already had the power to take extreme steps, the force wants them to know exactly what it expects of them if somebody in a vehicle is threatening lives.

"We don't want to wait until a car ploughs into a group of people. We want them to stop it before it occurs," he told reporters in Melbourne.

The force has also worked with the state government on changes to the Crimes Act which will reflect the policy's "absolute clarity" on the issue, he added.

Officers will undergo online and face-to-face training on the new policy from December, with all police expected to be up to speed by mid-2020.

Victoria is the first state to have a specific policy on responding to such attacks.

Almost a year after Gargasoulas's attack, Saeed Noori mowed down pedestrians on Flinders Street, killing an elderly grandfather and injuring 15.

In November 2018, Hassan Khalif Shire Ali drove a burning ute onto Bourke Street and fatally stabbed Pellegrini's Espresso Bar owner Sisto Malaspina and injured two other men.

The killer was shot at the scene by police and later died in hospital.

A vehicle was also meant to be used in a terror attack planned for Anzac Day 2015, which was stopped when uncovered by authorities.

Deputy Commissioner Patton said he didn't know whether the policy could have prevented the incidents.

"The fact is, our police officers, in a whole range of different scenarios, make split-second decisions that are then analysed over many years by people sitting and applying judgment in hindsight," he said.

"Our members, generally speaking, get it right."

But before a coronial inquest into the Bourke Street rampage - expected to begin next month - the deputy commissioner insisted the force was always eager to improve.

"We learn from critical incidents and that is why we've got this in place now."

Victorian Opposition Leader Michael O'Brien said he is surprised it took so long for the force to offer such direction.

"I wouldn't say it's too little, but I would say it's too late," he told reporters.

Australian Associated Press