HSBC said full service was quickly restored after some customers were temporarily unable to use their mobile banking apps on Friday.
The problem was the latest in a series of technical outages at British banks that have been criticised by lawmakers who said lenders had justified branch closures on the basis that they are providing a seamless online and mobile phone banking service.
The problem was identified at 0640 GMT, with normal service restored by 0800 GMT, HSBC said. Online banking, the use of debit cards and cash machines were unaffected.
"An earlier issue where some customers were unable to log on to the HSBC mobile banking app has been resolved and users of the app should be able to log on as usual," said a UK spokesman for HSBC.
"We will be conducting an investigation into the cause of this issue and we apologise for any inconvenience this may have caused."
Separately, TSB bank said it was aware that some customers were having problems using its mobile app and online banking services, and was seeking to fix the issue.