Vulnerabilities in Victoria's regional police radio system were exposed when a hacker interrupted the frequency during a car chase, the police minister says.

Impersonating an officer, the hacker interfered during a pursuit sparked by an alleged attempted armed robbery of shop on Tuesday evening at Sale.

The offender allegedly fled in a stolen car, also occupied by a woman, and police took chase.

"What we saw overnight ... highlighted the vulnerability of the current radio network system,' Police Minister Lisa Neville said.

It was an "appalling" act, but improvements to the network were already planned, she said.

Ms Neville says Telstra has been contracted to install base networks for a digital radio system used by regional police, the Country Fire Authority and Lifesaving Victoria.

The $12 million system should be fully operational by mid-2018.

Opposition police spokesman Edward O'Donohue said delays to the rollout put officers at risk.

"Our police are dealing with an unprecedented crime tsunami and the Andrews Labor government seems incapable of stopping it," he said in a statement.

The duo believed to be involved in the attempted robbery were pursued to the nearby town of Traralgon where the woman, a 22-year-old from Drouin, was arrested.

A 21-year-old Warragul man was later arrested on the roof of a nearby shed.

The pair are in custody and are being questioned.