Sheep on a property in northern Victoria have been vaccinated or killed after an outbreak of anthrax was detected, Agriculture Victoria says.

An anthrax outbreak at a farm in northern Victoria has prompted the killing of some sheep and vaccination of others.

Animal experts visited the farm, near Swan Hill, at the weekend after the contagious bacteria was detected in the sheep, the state's chief veterinary officer Charles Milne said.

The affected property has been quarantined, the sheep have been vaccinated and "appropriate disposals" have been made on Monday, Dr Milne added.

The naturally occurring bacteria is known to exist in soil across northern Victoria with several farms in the Swan Hill area affected in March 2017 and in March this year.

"Incidents tend to occur during the warmer months when it's drier and livestock forage deeper into the soil when eating grass," Dr Milne said.

Farmers should report anthrax symptoms in their livestock to the 24-hour Emergency Animal Disease Watch Hotline on 1800 675 888, their vet, or to Agriculture Victoria.