The NHS has issued a national “amber” alert over shortages of certain blood types in England.

A “perfect storm” has been created by “increased demand” of O type blood from hospitals and “reduced collections due to high levels of unfilled appointments at donor centres” in towns and city centres, reports NHS Blood Donation.

As a result of this, O negative and O positive donors are being asked to "urgently" book and fill appointments at donor centres.

This is just the second time an alert has been issued for blood donations, with the other announced in October 2022, according to Sky News.

The NHS Blood Donation website says NHS Blood and Transplant (NHSBT) has written to hospitals today to issue an "amber alert” asking them to restrict the use of O type blood to essential cases and use substitutions where clinically safe to do so.

Commenting on the blood stock alert, it explained: “Today, national stocks of O Negative are 1.6 days and overall national stocks of blood across all types is 4.3 days.

“On average, there are around 50,000 appointments to fill each week. There are over 12,000 appointments still to fill in donor centres over the next two weeks.”

Dr Jo Farrah, NHSBT chief executive said: “We urgently need more O group donors to come forward and help boost stocks to treat patients needing treatment.

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"Last month we saw an incredible response from donors who answered our call and filled up our centres, helping us meet the increased demands for blood throughout June.

"However, seven weeks on, the need for O negative blood in particular remains critical.”

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“We’re making an additional 1000 appointments per week available, please take a moment to go online and book.

"If you can’t find an appointment immediately, please book in for coming days, weeks and months.

"We will have an ongoing need for donations. Thank you everyone for your support.”