New teams of covert heavily-armed police officers will patrol Melbourne's streets and major events to enable a quick response to critical incidents such as terror attacks.

The new roving Critical Incident Response Teams will be pre-deployed at events such as the Australian Open and the Grand Prix and will be able to respond to threats in minutes.

Armed with sub-machine guns, handguns, Tasers and batons, the new teams officers will patrol the CBD and inner Melbourne in marked and unmarked vehicles from Monday.

Deputy Commissioner Andrew Crisp says the roving CIRT teams may save lives and were introduced in response to rising security threats globally.

"For us, timing is everything," he told reporters in Melbourne on Sunday.

"What we've seen worldwide over the past few years is a significant change in the security environment, and here in Victoria we are very conscious of that.

"I'm confident that if we can respond to incidents within a few minutes, as opposed to 10 minutes, we will save lives."

Victorians will rarely see the teams as they will remain covert until called upon but the specially-trained officers can be recognised by their darker uniforms, helmets and rifles.

"There's a rigorous selection process for them to get into CIRT," Mr Crisp said, but would not say how many officers were in place.

These kinds of officers already exist in Victoria but an expansion of the teams will be launched on Monday.

They will patrol the CBD every day of the year and will be pre-deployed at major events like the AFL Grand Final and the White Night Festival.

"We know these highly responsive teams are on par with global best practice and they will ensure the highest level of safety and security for the community," Mr Crisp said.