A lack of staff to care for people giving blood is thought to be behind the shortage in England.
Blood supplies have fallen to a critically low level in England, which has made NHS Blood and Transplant (NHSBT) declare its first amber alert.
Hospitals may have to postpone some elective surgery, but emergency care should not be affected.
A lack of staff to care for people giving blood is thought to be behind the shortage.
Overall blood stocks in the NHS stand at 3.1 days, but levels of O type blood have fallen to below two days.
The NHS is urging people to come forward and fill empty appointments at large donor centres. O blood groups are in particular need.
The public can go to blood.co.uk to check where appointments are available.
Blood supplies have been a challenge since the pandemic because of staff shortages, staff sickness and a change in people’s behaviour, which means they are less likely to visit donation centres in towns and cities, according to NHSBT.
Individual hospitals will have to decide how to manage the shortage of blood, but the types of surgery that could be postponed are all non-urgent, such as hip replacements.
These make up about 1% of all surgery, NHSBT says.
Hospitals will continue to carry out any urgent, emergency or trauma surgery, cancer surgery and transplant surgery.
The NHS usually has six days’ worth of blood stocks, but levels are currently due to fall below two days – the threshold for an amber alert.
As blood can only be stored for 35 days, there is a constant need for donations – and a need for specific blood types.