Coles has introduced national limits on egg purchases due to a growing bird flu outbreak in Victoria.

The highly pathogenic H7N3 strain of bird flu has been detected on five farms in the state's southwest, with more than half a million chickens euthanised
in an effort to stop the spread of the disease.

The supermarket giant's customers in every state and territory can now only buy a maximum of two egg cartons, with the exception of Western Australia.

Coles says the limit is temporary but has not revealed how long it is expected to last.