The website selling new millennial railcards has crashed due to high demand as just 10,000 went on sale.
Passengers across Britain aged 26-30 were eligible for the discount card for the first time on Tuesday.
But the website selling the cards was unable to cope with the rush of people trying to get hold of them.
A spokesman for railcard.co.uk said: "We've had an unprecedented number of people visiting our site for the 26-30 Railcard.
"Please bear with us, we've got the whole team working on it and hope we can have it back up shortly."
Chancellor Philip Hammond said in his Budget speech in November that the railcards would give "4.5 million more young people a third off their rail fares".
But only 10,000 are initially being made available while the scheme is trialled to assess the impact on revenue and passenger numbers.
The cards costs £30 each year and save a third off most fares.
Many passengers took to social media to express their frustration at being unable to buy the cards.
Emily Thomas, from London, wrote: "Getting a 26-30 railcard is worse than getting a Glastonbury ticket. Sort out your website to make it fair!"
In a message to the National Railcards Twitter account at 7.48am, youth worker Josh Booth, from Leeds, posted: "Been trying to get 26-30 railcard since 7am, your website crashing and been on hold on the phone since then."
Tom Drury, from London, wrote: "The launch of the new railcard is a shambles."
The card is aimed at leisure travellers, with no discounts on season tickets and a £12 minimum fare on all journeys between 4.30am and 10am, excluding weekends and public holidays.
It must be bought online and downloaded on to a smartphone.
The card was previously only available to a limited number of people in East Anglia.
A spokesman for the Rail Delivery Group, representing train operators, said: "Research being gathered as part of the 26-30 Railcard trial is being used to inform discussions with the Government about a national roll-out, and to develop new products that make leisure travel easier and better value for customers."