The building society has apologised and says it is "working to get things back to normal."
All payments to and from the Nationwide Building Society to other building societies and banks are delayed.
Money can still be moved between Nationwide accounts, it added.
Nationwide says customers can continue to use their cards online and in shops, log-in to their banking apps, and withdraw money at cash machines.
McDonald's blames global outage on third party.
As Virgin Money's directors agree to Nationwide's takeover bid, it marks an important moment in the decline of Scottish-based banking.
Why does the Bank of England change interest rates?
The Bank of England held rates at 5.25% for the fifth time, after 14 increases to tackle inflation.
Bank of England interest rates have an impact on the mortgage, loan and savings rates for millions of people.
A Dorset charity gives financial support to families struggling with money because of cancer.
'Jersey premium' on mortgages probed by watchdog.