The NHS website for booking Covid-19 vaccine appointments appeared to temporarily crash after people aged over 45 were offered jabs.
It is understood that a minority of people experienced issues with the service, including being unable to complete their booking, due to a surge in demand.
Some visitors to the site on Tuesday morning were faced with the message: “The NHS website is currently experiencing technical difficulties.
“We are working to resolve these issues. Thank you for your patience.”
Other users reported being placed in a queue, with a holding screen that read: “You are in a queue. Lots of people trying to book an appointment.”
Shortly after the vaccine booking site was hit by the technical issues, vaccines minister Nadhim Zahawi tweeted that the problem had been “fixed”.
It is understood that NHS Digital were able to get the website back up and running on Tuesday morning, with all issues being resolved and people able to book appointments.
NHS Digital tweeted shortly after 10am: “We are aware that some users are experiencing delays when accessing the vaccine booking service.
“We are working to investigate the issue as a priority and minimise the impact on service users.”
Technical teams worked to address the issue and users may temporarily experience longer waiting times and delay in receiving their booking confirmation.
One 47-year-old user from Bromley, south-east London, who only gave his name as Dean, encountered a problem as he tried to book a jab appointment at around 9.30am.
He said: “I seemingly booked, but the website crashed at the point of confirming contact details, i.e. giving phone number and email.
“Now, when I use my NHS number to check if my appointments exist, it will not let me find out without reference numbers for the (vaccine) bookings.
“But the paradox is, you need this from an email or text they would have sent.”
Dean was able to get back on to the website after it crashed for him, explaining: “It seemed to let me get to the point of checking my booking – but obviously this is impossible without a confirmation email/text.”
He tweeted at the official @NHSuk account, “hoping someone sees” to help him with the issue.
“I’ve already had at least four others say they have same problem,” Dean claimed.
He later said he had called the NHS on the 119 number and was given his reference numbers to access the booking system.
Dean said he was told that “many people are having this problem, (including) NHS staff”, that his appointments were booked, “the system is struggling” and that he should wait 24 hours to receive an email.
Jessica Rowbottom, 46, from Wakefield, West Yorkshire, also struggled to check her vaccine bookings after receiving no confirmation or reference numbers.
She said: “I work in website and application design and deal with user experience on a daily basis… it beggars belief it actually needs a confirmation number to access things anyway, especially when you’ve given the (date of birth) and NHS number in the first place.”
The technical issues came as the NHS online booking system opened up to allow people over the age of 45 to arrange for their coronavirus vaccine as part of the start of “Phase 2” of the vaccination programme.
The NHS has previously been focused on ensuring vaccines are offered to those considered to most vulnerable to coronavirus – those aged over 50, people deemed be “clinically extremely vulnerable” and health and social care workers.
There are an estimated 3.7 million people in England aged 45 to 49.
According to the Government, in total almost 40 million doses of the Pfizer and AstraZeneca vaccines have been delivered since their rollout began in the UK in December, including 32 million first jabs and more than seven million second doses.