Victoria police say the search for a man who shot and killed two officers will take longer than expected. 

The two men were gunned down on Tuesday while attempting to serve a search warrant at a rural property in Porepunkah - 300 kilometres outside of Melbourne. 

A major police operation is underway to find accused gunman Dezi Freeman - who could still be armed.  

Australian correspondent Murray Olds says hundreds of officers are tracking the suspect down - and helicopters are on the scene.

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