From 7am, a queue of 11,000+ was continuous on the booking site as people jumped to get their jab, which NHS officials have since described as a "Glastonbury-style" surge of traffic.
Those aged 25-29 in England were able to book for the first time yesterday, with 100,000 appointments booked every hour, NHS England has said.
Despite the issues which informed people they were not eligible, they were soon resolved and 493,000 appointments were reserved by midday, just five hours after over-25s were allowed to book.
In total, 1,082,596 first and second doses were booked throughout the day.
The head of the NHS in England said the figures have dispelled the suggestion younger people may shy away from vaccination.
Sir Simon Stevens, chief executive of the NHS in England, said: "Enthusiasm for the biggest and most successful vaccination programme remains strong as bookings for the lifesaving jab reached an all-time high yesterday and the obvious enthusiasm of younger adults to get their jab has blown out of the water the suggestion that people in their 20s might not come forward to protect themselves and their loved ones.
"The Covid-19 vaccine is still the best protection against coronavirus and as further supplies become available to us week by week it’s great that we’ve seen 25 to 29-year-olds sending bookings to blockbuster levels, following hard on the heels of the millions of others.
"Getting the lifesaving Covid-19 jab is the most important thing you can do, so book your appointment and get that vital protection. Remember: when you get the text, you’re next.”
NHS vaccine figures are released weekly, with the most recent figures released on June 3 recording a total of 14,300 jabs delivered to people aged between 30 and 39 as of May 30.
As of May 30, this means that around 33% of people between the ages of 30 and 39 have received a Covid vaccine.
Approximately 64% of residents in their 40s have been given their first dose, alongside 79% of residents in their 50s and 85% of those in their 60s.
Further vaccine figures will be expected tomorrow (June 10) with numbers up to June 6.