Thousands of London commuters may find their pre-paid Oyster does not work this morning, after a computer system crash disabled card readers across London.
The computer system went down for at least five hours on Saturday morning until around 9.30 am. Card readers across the buses, London Underground and trains such as Docklands Light Railway were not accepting Oyster cards for parts of the day.
Customers were allowed onto buses, tubes and trains during the glitch, however some cards used during that time have since stopped working or incurred a fine.
Retailers that sell and top-up Oyster cards were also affected and had their system restored online throughout Sunday.
Transport for London said the problem has been rectified and cards are now being accepted. However a "number of cards" may not be working as a result of the technical problem.
About 150 extra TfL staff have been in stations this morning (Monday) handing out replacement cards. It's been reported up to 40,000 cards could have stopped working after Saturday's fault.
Transport for London apologised and said people with a faulty card could get a replacement from Tube stations.
TfL said in a statement: "Customers whose cards are not working are advised to go to their nearest London Underground ticket office where they will be able to exchange their card for a replacement.
"A small number of Freedom Pass and Young Persons Oyster card holders may also have been affected. They will be required to apply for replacement cards through their relevant local authority and through the young persons' travel card helpline respectively."
All passengers who incurred a fare on Saturday 12 July will also be given a refund from Tuesday.
TfL is investigating the cause of the problem.