The NHS website for booking Covid vaccinations crashed on Tuesday as hundreds of thousands of young people queued to book nearly half a million slots in a "Glastonbury-style" rush.
Health service bosses saw an average of 100,000 vaccine appointments scheduled every hour on the first day of the jab being made available to 25 to 29-year-olds.
However, the surging demand caused the NHS site to crash for periods in the morning and saw people left waiting for more than an hour in queues of 10,000.
The NHS later said messages telling people they did not yet qualify for a jab were an error, urging those who had received them to try to book again.
The problems began early in the day, with people taking to social media to complain that they were waiting up to an hour online to get to the page where they could book their appointment.
Jacob Little wrote on Twitter: "Booking coronavirus vaccines on the NHS website this morning is like getting festival tickets … waiting in a queue, then the website crashes etc."
Users were soon facing mounting waiting times as more and people flocked to the site, with some reporting that they had been told there were 10,000 people ahead of them in the queue.
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Sir Simon Stevens, the NHS chief executive, said: "This encouraging Glastonbury-style rush for appointments has already now seen hundreds of thousands of people between 25 and 29 book in for their NHS Covid jabs as more vaccine supplies continue to come on line.
"Pleasingly, this suggests strong enthusiasm for vaccination amongst people in their twenties, following hard on the heels of the millions of others who’ve already taken up our offer."
When The Telegraph looked at waiting times on the site on Tuesday morning it was initially told it was 7,782nd in the queue, but that the estimated waiting time to get to the booking page was five minutes. Half an hour later the queue had whittled to 4,000 and the estimated wait time was still reported as five minutes.
When people did get through to the booking page, many reported then finding that the page had crashed, with a message warning that the site was "experiencing technical difficulties" and requesting them to come back later.
Others complained on social media that after they had put in their NHS number they received a message saying they were not yet eligible. Jack Crofts wrote on Twitter: "After waiting about an hour, the NHS vaccine booking portal crashed after adding my name and DOB. Trying again now, I’m 10,545th in line! Somebody please jab me."
A spokesman for the NHS said: "Large numbers of people are booking their vaccine appointments through the NHS website, which means you may need to wait in a queue. We know that some people have been receiving an ineligible message when trying to book, which is being fixed now – so please retry."
Vaccines were opened up to under-30s for the first time this week as the Government aims to offer all adults their first dose by the end of July.
Announcing on Monday that the rollout would begin for under-30s, Matt Hancock, the Health Secretary, told the Commons: "We have all been cheered by the images of so many young people coming forward and lining up to get the jab.
"It shows that the enthusiasm for the jab is not just the preserve of older generations but that the people of this country know what it takes to keep themselves and the people around them safe."