A perfect storm of record demand for blood over winter, coupled with cancellations, has left Australia's stock levels critically low.

Red Cross Lifeblood has issued an urgent call for donors as reserves of most blood types and plasma drop to critical levels.

An extra 12,500 donors are needed in the next seven days to ensure Lifeblood can continue to meet patient needs across the country.

Data show that demand for blood reached record levels in June, July, and August.

That demand surge coincided with the highest appointment cancellation rates since the COVID-19 pandemic, severely impacting the supply of multiple blood types.

Lifeblood CEO Stephen Cornellison said it wasn't unusual to see a spike in cancellations and lower appointment bookings during winter, due to people contracting colds, the flu, and Covid-19.

But this winter hit particularly hard.

"We experienced our highest ever winter demand for blood, which has significantly impacted Lifeblood supplies," Mr Cornellison said on Tuesday.

"We're urging anyone who is eligible and feeling healthy and well to book a donation immediately and help restore our blood stocks.

"Right now, we need donors of all blood types. If you've never donated before, now is the time to start."

A blood donor is needed every 18 seconds in Australia to help patients undergoing cancer treatment, major surgery, trauma, pregnancy and childbirth, and a range of other conditions.

Just one blood donation can save up to three lives.