Sharecast - Thousands of the bank’s customers reported issues accessing their accounts, with complaints appearing on X - formerly Twitter - and platforms such as Downdetector.
Downdetector, which aggregates reports of issues with online services, reported a spike in complaints just before 0900 GMT.
The bank acknowledged the inconvenience caused to its customers and attributed the disruption to an “internal system issue”.
It said the problem only impacted HSBC UK customers, with no reported impact on its First Direct or M&S Bank operations customers.
The BBC reported that the exact number of affected individuals was unclear, as users would need to check their online banking apps to confirm whether they were affected by the issue.
HSBC has around 14.8 million customers across the UK.
At 1127 GMT, shares in HSBC Holdings (LON:HSBA) were down 0.78% at 606.9p.
Reporting by Josh White for Sharecast.com.
