Thousands of Santander customers are unable to use mobile and internet banking or its app because of 'technical issues'.
Customers across the country are reporting they are unable to log in to their banking online.
They say they have been unable to use their cards and have had payments rejected in supermarkets.
The bank said it is trying to fix the problem as soon as possible and will update its customers via social media. It said it does not have 'any timescales at the moment'.
Thousands of Santander customers are unable to use mobile and internet banking or its app because of 'technical issues'
Santander said: 'We are currently experiencing technical issues, we are working hard to resolve.
'Apologies for any issues this causes.'
It said it had maintenance planned on its online and mobile banking from Friday to Sunday between 9pm and 6am.
The bank added: 'We're experiencing very high volumes of calls into our contact centres.
'Please help us to protect our services for those of our customers who are most in need.
'If your call is not urgent please use our online and mobile banking services, our online chat facility or review the information available on our website.'
Responding to a customer complaint on social media, it said it is 'working hard' to fix the problem.
It said: 'Regrettably, we currently don't have any timescales at the moment.
'Rest assured we're working hard to help resolve the matter and once we have any updates, our customers will be the first to know.'