Supplies of O-Negative blood are low and an appeal has been made for donors with the blood type to arrange to give blood.

Supplies of O-Negative blood are "down to the last few drops" and donors with the blood type are being urged to arrange to donate this week.

"Due to some extraordinary circumstances, we had some very ill patients in hospital who required a lot of O-Negative blood," NZ Blood Service national manager of marketing and communications Asuka Burge said.

Last week the service emailed and texted donors on its books with O-Negative blood asking them to arrange to donate. Yesterday Facebook appeals were made for donors in the north of the country and Waikato to donate.

"We've had a great response so far from the call and have started to book in for this week," Burge said. We're hoping the response is going to enable us to recover those stock levels back and make sure we can continue to meet demand."

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Only about 9 per cent of people had O-Negative blood. "It's the universal blood type, so in an emergency they don't need to blood-type the patient to give them this blood. Anyone can receive O-Negative in an emergency situation."

The blood service is highlighting the lack of O-Negative blood at the top of its website.

"We are down to the last few drops of O-Negative blood," it said. "If you're O-Negative we urgently need you to donate blood to save lives now."