NatWest customers are currently unable to access their bank accounts through the company’s online and app platforms.
Since around 5am on Friday, account holders have been reporting problems with the service.
The app shows an error message that says it is “unable to establish a connection”, while the bank’s website displays a message saying that online banking is “temporarily unavailable”.
NatWest said it was “working hard” to fix the online and mobile problems.
It added that telephone banking and ATMs are available.
“Sorry and thanks for your patience,” the bank said.
Customers have been sharing their frustration on social media, with a number affected on payday.
The bank had a similar problem in April last year, when both RBS and NatWest banking apps stopped working.
RBS Group, which owns NatWest, reported last year that it had over four million customers who use its mobile app services.