The Blood Service is urging people in good health to book in and give blood as the squeeze could go on under peak Omicron, with thousands of people catching the virus or having to isolate as contacts.
It is struggling with supplies as thousands of potential donors are sick with Omicron or isolating at home and unable to donate.
Asuka Burge from the New Zealand Blood Service said people recovering from Covid can donate after they have been free of symptoms for 14 days.
The service needs 4000 donations each week and currently has 12,000 appointments to fill this month.
"We know that we're not immune to the impact of Omicron and this is starting to have an impact on the eligible donors able to donate."
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Burge said you cannot donate blood if you have a cough or cold or if you are isolating at home because someone in your household is a confirmed or suspected case of Covid-19.
"We're really asking people who are eligible, who are healthy, to check if you're eligible, book in to donate so that we can actually build our blood stocks up and boost that supply now while we can."
Burge said donated blood only lasts 35 days and demand is constant.
She said the Blood Service also has mobile community drives and it is possible to download their app to find out when they might be near you and book in.
"Every donation counts and we really want to make sure that that blood is there on the shelves when it's needed and that's why we're calling on the people to book now."
Burge said people can donate blood every three months or 84 days and people who donate plasma, which is also important, can do so every fortnight.