NatWest to open all weekend as problems persist
Thousands of NatWest accounts are still affected by computer problems, leading the bank to take the unusual step of opening on Sunday for customers.
While it says the underlying computer failure has been resolved, there is still a massive backlog to deal with.
Overnight payments were still not appearing on balances, leaving some unable to access wages.
Some RBS and Ulster Bank accounts have also been affected, but NatWest says no one will be left out of pocket.
NatWest and Ulster Bank are part of the RBS group.
NatWest says more than 1,000 branches will be open until 19:00 BST on Friday. Branches normally open on Saturdays will extend opening until 18:00.
Saturday branches will also open on Sunday from 09:00 to midday.
NatWest, which opened 1,000 branches early at 08:00 on Friday, apologised for the "unacceptable inconvenience".
Emergency cash may be made available as people are left out of pocket. Some have had to delay completing purchases of homes and others have reported concerns about getting money for the weekend.
In a statement on the NatWest website on Friday, the bank said: "We are continuing to experience technical issues with our systems.
"As a result, money credited to accounts overnight may not be appearing on balances today. This problem is strictly of a technical nature and we are working hard to fix it as soon as possible.
"Staff in our branches and at our call centres are ready and available to answer any questions. Staff in branches will also be able to assist impacted customers who need access to cash."
The problem is understood to have arisen after staff tried to install a software update on RBS's payment processing system, but ended up corrupting it.
The underlying technical issue has now been resolved, according to a source within RBS.
However, the inconvenience to customers is likely to continue as staff try to clear the backlog.
The weekend will provide a breathing space to update payments in and out of accounts, although there is no guarantee that everything will be back to normal by Monday.
Most of the payments which had been missed on Wednesday night have now been processed, but many of Thursday night's payments have not got through. However, delays are worse at Ulster Bank.
Customers could still use cash machines as normal.
One account manager from Hertfordshire told the BBC that she could not make payments to suppliers or staff as a result of the problems.
"It also does not help that this has happened at a time when we are all having to leave things to the last minute to pay, because cashflow is so tight," she said.
"There are some people I should have paid and promised payment to on Wednesday. Not being able to honour those promises will have an impact on their cashflow too."
NatWest has 7.5 million personal banking customers and said a large number had been affected. Ulster Bank said earlier that 100,000 of its customers had been affected.
The Financial Ombudsman Service said that anyone affected should keep a record of how they were left out of pocket. Banks are obliged to return affected customers to the position they should have been in had the problem not occurred.
A spokeswoman for UK Payments Council, which oversees payments strategy, said that the problem did not appear to have affected any other banks.
However, people expecting payments from individuals or businesses which banked with NatWest could encounter problems.
The Financial Services Authority, which regulates the banks, said: "We are aware of the technical problems RBS-NatWest is having.
"They have kept us fully informed and are working hard to resolve the problem as quickly as possible. They are keeping customers updated through their website and have call centre and branch staff on hand to help with any queries."