Sightings of locusts in central west NSW have prompted authorities to warn farmers to be vigilant as they prepare to harvest winter crops.

But while there might be local hot spots the threat of a widespread outbreak of locusts is minimal according to the experts.

Chris Adriaansen, Director of the Australian Plague Locusts Commission, says the number of locusts is extremely low as seasonal conditions have been too hot and dry.

He says for the numbers of locusts to breed up to any significant levels, "that would require a lot of rain, a lot of fresh pasture growth and about six months for 2 or 3 successful generations of breeding".

Chris Adriaansen says given all that, he does not expect to see any significant numbers of locusts this spring or summer, anywhere in Australia.

"The earliest we could see any significant locust numbers would be next autumn.

"We have been monitoring for the last six weeks throughout Victoria, South Australia, NSW and Queensland and the presence of locusts has been very small.

"We think the low numbers are also result of pesticide control and biological control last year.

In the Central West of NSW though, bands of moving locusts and locust nymphs have been seen in the region and farmers are being urged to carefully check their crops and pastures for the insects.

Senior Ranger with the Central West Livestock Health and Pest Authority, Lisa Thomas says the locusts are a worrying sight.

"We can't afford to have crop losses now, the crops are certainly precious. What the locusts eat, again, is going to impact on your pocket.

"Outside the consequences of them laying and having a second generation, which is very likely starting so early now, they'll be second and third generation by the time they've really cleaned you out."