Victorian police will be given stronger legal protection to shoot to kill suspected terrorists under powerful new laws in response to the deadly Brighton siege.

The Andrews Government also plans to give police the power to hold terrorism suspects for up to four days without a court order.

The changes are based on a review of the state's counter-terrorism laws by former police chief commissioner Ken Lay and retired judge David Harper.

Since September 2014, Victoria Police have charged 39 people with terrorism offences, 19 of whom have been convicted.

Officers are also monitoring 300 "persons of interest" who have been identified as posing a potential security risk.

Mr Lay and Mr Harper recommended 16 legislative changes after gunman Yacqub Khayre was killed during a siege and attempted terrorist attack in Brighton in June.

While police already have shoot-to-kill powers, the law will be clarified to give officers greater confidence using pre-emptive lethal force.

The report warned that any hesitation by police "may cost innocent lives, or otherwise fail to avoid the harm that it is the duty of the police to prevent".

"Waiting for absolute certainty or overt signs that the risk of harm is imminent may be inconsistent with the response that good policing requires and indeed result in a catastrophe," it said.

'Hesitation can cost lives'

Victoria Police Chief Commissioner Graham Ashton said officers confronted by suspected terrorists must not feel unduly restrained.

"In this day and age there's a need to act very quickly and seconds count. We're more likely than ever to have to shoot first," he said.

"We can't allow any uncertainty to creep in. We're coming up against better armed and equipped offenders all the time."

Following Sydney's Lindt cafe siege, the New South Wales coroner also recommended changes to ensure that police had sufficient legal protection to respond to terrorism attacks

The Victorian Government plans to extend the preventative detention period for suspected terrorists from two to four days, after which they will be able to apply to the Supreme Court for a two-week extension.

For the first time, police will be able to question people being held in preventative detention.

"Police will need to exercise great caution to ensure that any period of interim detention is no longer than is absolutely necessary," the report said.

There will be a presumption against bail and parole for anyone facing terror-linked charges or who has shown support for a terrorist group.

Police will also be able to declare "special areas" in the event of a terrorist attack, giving officers the power to search people, cars and property without a warrant.

Khayre was on parole when he shot dead receptionist Nick Hao in a bayside apartment building, took a sex worker hostage and fired at three officers.

He was killed in a shoot-out with police.

'That's the modern world'

Premier Daniel Andrews was unapologetic to the argument the laws were an unjustifiable intrusion on civil liberties and human rights.

"If it comes to a question of curtailing the rights of a small number of people to protect tens, perhaps hundreds of thousands of other Victorians, then I won't hesitate to make that call," he said.

"That's the modern world we live in."

Opposition Leader Matthew Guy expressed support for the changes and called on the Government to introduce them soon.

"The police need these laws to keep us safe, it's as simple as that. We need to put Victorians security and safety first," he said.

Mr Lay described the powers as "extraordinary" but necessary in the face of the significant threat posed by terrorism and violent extremism.

The changes will be discussed at a special Council of Australian Governments meeting next month.

Mr Andrews indicted a post-custodial monitoring regime for terrorists would be detailed in a second report due in weeks.