Health officials are appealing for new blood donors to come forward after a "dramatic decline" in the number of younger donors.
NHS Blood and Transplant (NHSBT) is attempting to recruit 100,000 new donors in the next 100 days.
A spokeswoman said 17 to 24-year-olds are "vital" to the blood service, accounting for around 40% of new donors each year.
But so far this year there has been a 50% drop in the number of 17 to 18-year-olds registering compared to 2011.
NHSBT spokesman Jon Latham said: "The number of young people donating has been falling for the last decade but this year there's been a sharp drop.
"We welcome new donors of any age, but a failure to boost the number of young donors now will put a strain on the blood service in the years to come."