In response to the rodent plague around the state, the NSW government announced earlier in May that it would roll out a $50 million assistance package.

Under the plan, farmers will be offered free baits as well as rebates of up to $500 per household, and $1000 per business through Service NSW.

Vice president of the NSW Farmers Association, Xavier Martin, said the assistance may have come too late to be effective.

"The state government's assistance package is impractical, dysfunctional, and weeks away, which is not helping farmers who need support right now to drive mouse numbers down and break this horrible unrelenting cycle," Mr Martin said.

With preparations for the winter crops underway, Mr Martin said there was significant concern that the window of action was rapidly closing.

"Farmers are abandoning some paddocks and cannot hold off winter crop sowing a moment longer and researchers warn that without a concerted baiting effort in the next few weeks this could easily turn into a two-year plague event," Mr Martin said.

"After more than eight months of battling growing mouse numbers, farmers are still waiting for state government assistance to hit the ground and offer some practical support to our farming community.

"Each day we delay in taking effective action to control these mice will increase economic losses and the likelihood we will still be battling mice come Christmas time."

During senate estimate hearings on Wednesday, secretary of the federal department of agriculture, Andrew Metcalfe said there were no plans to roll out a nationwide response to the plague. According to the government's Mouse Alert website, rodent populations are now affecting parts of Queensland, NSW and Victoria.

"Very long-standing arrangements are that each state and territory is responsible for pests and animal management within its jurisdiction," he said.

Mr Metcalfe also disclosed problems regarding the access to zinc phosphide chemicals used in the making of effective baits.

Most of the zinc phosphide is manufactured in India, leading to supply problems in the midst of the pandemic crisis.

"One of the other issues is, of course, the availability of the precursor chemicals for the baits," Mr Metcalfe said.

"We know that Australian bait manufactures are having to largely use zinc phosphide as the major chemical and there's a lot of pressure on that chemical given the rising level of demand for it."

Riverina representative of the NSW Farmers Association, Alan Brown, told The Daily Advertiser there is mounting anxiety over the shortage in zinc phosphide.

"There is no end in sight, usually with mice they'll run out of feed and cannibalise and the population will crash, but that doesn't seem to be happening," Mr Brown said.

"They're still breeding and farmers have a great deal of concern for the future. We haven't suffered the drought as much as some have, then they get one good season and they've got a mouse plague to deal with."

Meanwhile, the government's rollout of the bromadiolone chemical has been delayed by approval processes with the Australian Pesticides and Veterinary Medicines Authority (APVMA).

The chemical was described by NSW agricultural minister Adam Marshall as being equivalent to napalm for mice.

NSW Farmers are now calling for rebates of up to $25,00 per farm business to cover privately accrued costs.

"We're still happy the government is recognising there is a problem, but we're unsure of what the benefit will be [to the funding package]," Mr Brown said.

"Some have already spent a lot trying to keep mice out and there's been no recompense."

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