Customers and businesses who bank with HSBC UK are facing disruption on one of the busiest days for online purchases after the lender’s mobile and digital services were hit by an outage.

The group said it was investigating the situation “as a matter of urgency” after thousands of customers complained of problems with online banking.

The disruption is a blow because it has coincided with the annual Black Friday shopping event, when consumers flock online for deals before Christmas. According to Downdetector, a service that tracks outages afflicting web services, more than 4,000 people had reported problems with HSBC UK’s online services.

The problems started just after 8am on Friday and HSBC could not say how many customers had been affected.

A spokeswoman for the bank said the problem had been caused by “an internal system issue” and that the disruption was to customers of its HSBC UK arm, rather than its First Direct brand or its M&S Bank joint venture.

HSBC UK also apologised to customers on Twitter/X for the problems and said: “We’re working hard to restore mobile and online banking service, and the authorising of online card purchases via the app. We’re really sorry for the inconvenience.”

Customers took to the platform to vent their frustration with the bank. “Pay day and I can’t pay my bills and organise my money,” one user wrote.

Sam Richardson, deputy editor of Which? Money, said: “This HSBC outage will cause a real headache for a lot of its customers. In the worst cases it could prevent people making essential payments such as rent and bills, but it also falls on Black Friday, one of the busiest shopping days of the year, where many people will be looking to make significant savings on big-ticket items.

“We strongly advise customers that have been left out of pocket to keep evidence of extra expenses they may have incurred as a result of the outage, so they can be claimed back from HSBC.

“People want a bank they can depend on, and if IT outages become a regular occurrence, consumers could be tempted to vote with their feet and switch to an alternative provider – particularly with a lot of tempting switching incentives on offer at the moment.”

Protecting digital services from outages caused by glitches or cyberattacks has become a priority for banks and other companies as services across the economy have increasingly moved online. Ensuring the so-called “operational resilience” of key services run by banks and building societies is a significant focus for regulators at the Bank of England.

The FTSE 100 bank, which is based in London, is Europe’s biggest bank by assets.