As locals in a Western Australian town battle a siege of mice, farmers still do not have permission to use a high-strength bait to combat them.

A severe mouse plague is overwhelming towns north-east of Perth, with residents describing roads covered in mice and infestations in homes and businesses.

Locals and farmers say current baits are ineffective and are calling for urgent approval to use stronger rodent poisons — a bureaucratic process that is dragging on.

The local MP says in the meantime, people are leaving town.