Racetracks across Australia were all but shut down Saturday, the country’s richest horse race is in doubt and losses could total more than a billion dollars after an outbreak of equine influenza.

The highly contagious equine virus was discovered in 11 non-racehorses at the Centennial Park complex adjoining Sydney’s Royal Randwick racecourse. Five horses at a second Sydney facility also showed symptoms of the disease.

Racing was canceled Saturday across Australia except on the island state of Tasmania and in the Northern Territory as agriculture officials expanded to 6 miles an exclusion zone around the Centennial Park stables and banned all movement of horses within New South Wales state.

New Zealand officials later banned imports of Australian horses, and the Melbourne Cup, traditionally held on the first Tuesday in November, was in danger of being postponed