Barclays is urgently looking into "technical issues" affecting its web and mobile banking services and debit card users.
Customers have been contacting the high street bank on social media to say they have been having problems accessing their money and making payments.
In a tweet from its @BarclaysUKHelp account, the bank said: "Some customers are experiencing technical issues affecting our website, mobile banking & debit card usage. We're urgently investigating this."
Customers took to Twitter to ask for help with problems.
Rohit Kahlon wrote: "@BarclaysUKHelp unable to use my card to pay or withdraw money even though there's money in my account?"
Jamie Lewis voiced his frustration, telling the bank: "Can't pay for fuel, nice one."
And Gary Lodge wrote: "@BarclaysUKHelp @BarclaysUK how long is this gonna take i'm stuck and cannot get home. This needs to be sorted."
A Barclays spokesman said: "We're aware that some customers are experiencing technical issues affecting debit card usage. We're urgently investigating this and apologise to customers for any inconvenience caused."