Lloyds Bank, Halifax and Bank of Scotland have seen their online services go down following an outage at Amazon Web Services (AWS).
The outage, which was reported just after 9am in the UK, is also affecting a number of widely-used apps, such as Snapchat, Signal and Zoom as well as crypto exchange Coinbase and even His Majesty's Revenue and Customs.
A status update on the AWS website posted just after 10.00am UK time states: "We have identified a potential root cause for error rates for the DynamoDB APIs in the US-EAST-1 Region... We are working on multiple parallel paths to accelerate recovery."
Downdetect, a website the monitors platform outages, has reported that thousands of customers of UK banks are experiencing problems with card payments as well as the inability to access their online bank accounts.
Amazon's cloud service serves as the backbone for a host of apps and online services including a number of high street banks in the UK.
It is not the first outage to affect banks this year. In February, more than 1.2m customers of four banks - Lloyds, TSB, HSBC and Nationwide - were affected.
Meanwhile, a report published by the UK Treasury Committee in March calculated that outages suffered by UK banks over the last two years amount to more than two months.
At the time of writing, no statements had been issued by the affected banks.