Australians are being urged to roll up their sleeves as the nation's blood supplies reach dangerously low levels.

The Red Cross says it has less than three days' supply of blood left across Australia and is appealing for donations.

All states are in critical need of donations, but the situation is particularly dire in Western Australia, which has less than a day's worth of blood remaining.

Only Tasmania, the Northern Territory and the ACT have more than three days' supply available.

Blood Service spokeswoman Kathy Bowlen says the low supply of O-negative blood is particularly concerning.

"O-negative is the universal blood type, it can be given to any person, in an emergency, regardless of what type their blood is," she said.

"It's the type we always need on stand-by in an emergency department in hospitals and at the moment in the three bigger states, we've got just over one day's supply."

The Red Cross says stocks are urgently low because just one in 30 Australians are rolling up their sleeves to donate blood.

Ms Bowlen says it has been a difficult year for donations.

"Australia relies on just 3 per cent of the population who are blood donors, and the interesting thing is most people decide to become blood donors after they've been touched by the need for blood," she said.

"Thirty per cent of all blood we collect goes to cancer patients so if you know anyone who's had treatment for cancer, the chances are they've received blood products, and a lot of their relatives or friends then decide to become blood donors, but we need more people."