Monster storm threatens 20 pct of Australia's wheat crop

SYDNEY, Dec 1 (Reuters) - Heavy rains in eastern Australia forecast to intensify over the weekend could wipe out or damage up to 4 million tonnes of wheat due to be harvested shortly, forecasters said on Friday.

Most of the state of Victoria and parts of the states of South Australia and New South Wales were facing a "major weather event" in the coming days from torrential rains, according to Australia's Bureau of Meteorology.

"The main concern is that these are the areas where crops are still being harvested," said James Maxwell of Australian Crop Forecasters, which expects to downgrade its national wheat forecast of 21.7 million tonnes once the damage is assessed.

"At the moment, we estimate that around 4 million tonnes will be affected," Maxwell said.

It was not yet possible determine how much of the crop would be wiped out and how much is downgraded due to the onset of re-sprouting, or premature germination, resulting in lower yields.

Victoria could see the loss or damage of up to 1.7 million tonnes, according to Maxwell. Farmers there have worked continuously to strip as much grain off the crops as possible resulting in just over 25 percent of this season's crop of 3.4 million tonnes already being harvested.

In New South Wales and South Australia combined the figure for losses could reach as high as 1.9 million tonnes, Maxwell said.

Bureau of Meteorology forecaster Scott Williams said the rain would fall heavy and fast, with the potential of more than 50 millimetres (1.97 inches) in just an hour.

Rainfall in excess of 250mm is forecast by the Bureau of Meteorology for parts of eastern Victoria, with the overall state expected to see more than 60mm.

Victoria's state premier, Daniel Andrews urged people to brace for a "very challenging period" over the next few days.

"This is a very serious matter, and one that will pose a real challenge to communities right across the state and will be a direct challenge to public safety," he told reporters.

(Reporting by James Regan; Editing by Christian Schmollinger)