Some Royal Bank of Scotland (RBS) and NatWest Bank customers cannot access online services as the banking group experiences a computer problem.
RBS and NatWest are part of the same group and they share many systems.
According to Sky News a large group of people had gathered outside a NatWest branch in Reading after failing to access their accounts.
A statement from the banking group said: "We are currently experiencing technical issues which mean that a number of customer account balances have not yet been updated and some of our online services are temporarily unavailable.”
In the statement, the firm apologised to customers and said the bank is working to fix the problem.
In November last year customers of the two banks were unable to access online or telephone banking over a weekend after maintenance issues.
A glitch in a regular maintenance update on the Saturday took the banking services offline over the weekend. ATM machines and credit card payments were unaffected.