The Irish Blood Transfusion Service has appealed for more regular blood donors as supplies for some blood groups have fallen to just three days.
The IBTS is especially seeking donors with Rh Negative blood groups (O-, A- or B-).
High demand from hospitals, an increase in illness among donors and bad weather conditions have all combined to create a shortage, the IBTS said.
Paul McKinney, Director of Donor Services and Logistics at IBTS, said: "A pre-amber alert has been issued in line with the National Blood Shortage Plan for the Rh- Negative blood groups, which requests conservative use of blood by all hospitals.
"All donations are needed to avoid any impact on our hospital system. We are asking our regular donors to make an extra effort to book an appointment and donors in Dublin to consider booking an appointment at our fixed centre in D'Olier street."
Donors can book an appointment online at www.giveblood.ie or phone 1800 731 137.
