The National Lottery website crashed as thousands of people logged on to the site ahead of Wednesday night's £50.4m jackpot draw. The biggest-ever jackpot in the UK has prompted a surge in ticket sales.
Camelot said that they expected to sell 200 tickets an hour before sales close at 19:30 GMT ahead of the draw at 20:30 on Wednesday (6 January).
However, many hopeful punters were greeted by a message saying that the website was "temporarily unavailable" because it was "extremely busy". Users of the site were urged to "try again shortly" as the deadline loomed, Sky News reports.
Many will be disappointed if they miss out on the chance to be in the draw, which could create one of the biggest winners in the lottery's history.
If no one wins the jackpot it will roll over and either be won or shared on Saturday (9 January), Camelot said. If no one gets six lottery numbers on Wednesday or Saturday, new Camelot rules mean the jackpot prize will be shared out in the first draw after the prize reaches £50m.
Dr Rob Mastrodomenico, a statistician and founder of the consultancy Global Sports Statistics, said the record prize was the result of the increased number of balls – 1 to 59 – which had reduced the odds of people selecting winning numbers.
The previous largest jackpot was £42m, which was shared between three separate ticket holders in January 1996. The biggest individual winner was Iris Jeffrey from Belfast who won £20.1m in 2004.