NatWest said it had failed overnight to solve issues that meant some customers’ accounts were not updated reports The BBC.
“Unfortunately we are once again experiencing technical issues with our systems,” NatWest said on Friday.
As well as some NatWest customers, others with RBS and Ulster Bank accounts have also been affected.
NatWest and Ulster Bank are part of the RBS group.
NatWest, whose branches opened at 08:00BST, apologised and said customers would not be left out of pocket.
In a statement on the NatWest website on Friday morning the bank said: “Unfortunately we are once again experiencing technical issues with our systems and account balances have not updated properly overnight.
“This means where money has gone into a customer’s account, there may be a delay in it appearing on their balance.
“We can assure our customers that this problem is strictly of a technical nature and we continue to work hard to resolve this.”
Some branches had stayed open late on Thursday to help customers on their way home and staff continued to work through the night.
Earlier, NatWest confirmed that a number of business accounts had also been affected.