Visa, the payment systems giant, has said it is experiencing problems processing some transactions in Europe.
"Visa is currently experiencing a service disruption," the company said in a statement on Friday.
"This incident is preventing some Visa transactions in Europe from being processed," it added.
"We are investigating the cause and working as quickly as possible to resolve the situation."
Consumers in Britain, Ireland and other European countries reported on Friday being unable to use their Visa cards.
Payment processing company Paymentsense says transactions are starting to go through after a period of disruption but "there is still some intermittency."
It encouraged customers to try contactless transactions as they had "a better chance of going through".
