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Two of Australia's top races have been postponed until next week after a torrential storm flooded Flemington racecourse within 20 minutes.

Jockeys agreed they were lucky one of the three Group One races of the day, the Newmarket Handicap, was run without incident just minutes before the hail storm struck with three races remaining.

The other Group One features, the Australian Guineas (1600m) and the Australian Cup (2000m), were consecutive races after the Newmarket but the deluge was so severe that stewards called off the meeting more than an hour after the Guineas' scheduled starting time.

The storm was likened to the deluge which flooded Flemington before the 1976 Melbourne Cup won by Van Der Hum, except there was no hail then.

The weather bureau yesterday reported 19mm of rain fell in 18 minutes before the storm struck.

Racegoers ran to higher ground as the water flooded all parts of the track while horses took fright in the stabling area of the course with several breaking free.

Chief steward Terry Bailey said Victoria Racing Club officials as well as jockeys were consulted before his panel formally declared the track unsafe for racing.

Champion jockey Damien Oliver said there was 25mm of ice on the track and another 50mm of water.

Fellow jockey Dwayne Dunn said the flooding brought back memories of his days riding in Malaysia.

"I have never seen a track this wet with the surface water being so high except for Penang when I was there and they had 26 inches for the week," Dunn said. "The thunder was getting close, and when coming down the straight there were three or four lightning strikes".

The Mike Moroney-trained King Pulse, who ran fourth in the Newmarket, broke away on the way back to the stalls area and fell twice suffering suspected internal injuries as well as lacerations and bruising.

Newmarket winner Wanted also broke free but was quickly picked up.

The Gai Waterhouse-trained Gigas was another who took fright and got away from her handler, running free before being caught.

Five Car Stud broke down during the running of the Newmarket and won't race again.

- AAP