CSIRO says farmers have reported increased mice activity in northern NSW, central Queensland, north western Victoria, the Yorke Peninsula in South Australia and the wheat belt in Western Australia.

CSIRO research scientist Steve Henry told AAP it can be difficult to notice growing numbers of mice before it becomes too late to combat them.

"Farmers need to get out of their vehicles and walk through their paddocks to see signs of mouse activity," Mr Henry said.

"We haven't reached plague proportions but we are getting reports of higher numbers across the cropping zone and farmers need to be prepared to take action to reduce numbers as they sow the winter crop."

Millions of dollars worth of crops were destroyed during last year's mouse plague in NSW and southern Queensland, which also caused extensive damage to farm machinery, vehicles and buildings.

Mr Henry said mice are most likely to be in the unharvested summer crops, and in the winter crop stubble where grain has been left behind.

"As it gets colder mice are also seeking shelter and are coming into houses and other buildings," he said.

NSW Farmers Vice President Xavier Martin has urged farmers to survey their properties for signs of rodent activity in a bid to avoid a repeat of last year.

"Let's make sure we all get out of the ute and into the paddock to make sure we avoid another plague," he said on Monday.

Some farmers have increased baiting in a bid to suppress mice numbers.

The NSW government introduced a rebate for zinc phosphide bait last year.

CSIRO data indicated patchy numbers of mice across NSW but Mr Martin said farmers were reporting more rodents running around their properties.

"What we don't want to see is a repeat of last year's mouse plague, so please if you see something, say something," he said.

One third of farmers surveyed by NSW Farmers estimated their losses at between $50,000 and $150,000 during last year's inundation.

Australian Associated Press