Victoria Police have announced an unprecedented reward of $1 million dollars for information leading to the arrest of alleged cop killer Desmond Freeman.

The reward is the largest ever offered.

The record bounty comes as police enter their day 12 in their search for the alleged killer.

Despite hundreds of tip-offs, there have been no confirmed sightings.

Freeman is believed to be heavily armed as police continue to search over 100 properties and acres of bushland.

Police have previously stated that they believe some people might know his whereabouts or are potentially harbouring the alleged killer.

Authorities remain open to the possibility that Freeman is still alive or could potentially be dead as a result of self-harm.

They hope this reward for information leading to his arrest will be an incentive.