Mice have been spotted streaming across roads in parts of NSW, concerning farmers and researchers as rodent numbers surge in other parts of the country.

NSW Farmers president Xavier Martin said he observed mice “swarming all over the road” near Coonabarabran in the Warrumbungle Shire.

“The worst of it was probably at least half a kilometre long,” Mr Martin told AAP.

“I came into some big patches where there were hundreds of mice running backwards and forwards in different directions looking for food.

“Members are telling me they’re seeing mice again all the way from Queensland down to the Victorian border and out west towards Adelaide.”

Mr Martin has received reports of damage to crops and fodder across the state, and urged farmers to remain vigilant. 

“We’ve got mice at the moment damaging our sorghum crop, and no doubt damaging other farmers’ summer crops and fodder,” he said.

“They’re getting into hay sheds and we’ve just got to hope we can get on top of them, and not let them develop like they did two years ago.”

He urged farmers to use chew cards to record mice numbers. 

CSIRO research officer Steve Henry said reports of mice swarming were a cause for concern.

“When you see them running over the road like that, that means they’re at peak population in the paddocks,” Mr Henry said.

CSIRO researchers have been trapping mice across the country over the past few months, with numbers on the rise in the south of Western Australia, and on the Yorke and Eyre peninsulas in South Australia, as well as the central west and north of NSW.

Mr Henry urged farmers to stay on top of their baiting program so mice numbers did not return to 2021 levels.

Farmers estimate the 2021 mouse plague caused millions of dollars worth of damage to crops and infrastructure.

By Liv Casben in Sydney