The Australian Plague Locust Commission says egg beds up to nearly 20 kilometres long have been exposed in north-western Victoria after the recent flooding.

Commission director Chris Adriaansen says heavy rain has washed away top soil and revealed the extent of egg-laying in those regions.

He says it is unlikely the water will destroy many of the eggs.

"The majority of those eggs, even those that are just below the surface are still likely to survive and hatch, but progressively we will see some of those eggs hatching a little earlier than would normally be expected because of that exposure to the accumulation of heat," he said.

Yesterday a three-kilometre long bed of locust eggs was discovered west of Nyngan in central New South Wales.

New South Wales Ranger Lisa Thomas said the eggs were expected to start hatching quickly as the weather warmed up.

The locusts are expected to devastate crops in Victoria, New South Wales and South Australia when they hatch.