National Australia Bank (ASX: NAB) says its telephone and internet banking services which were interrupted earlier today have now been fully restored and are functioning as normal.

At around 8.40am the telephone banking system began experiencing issues which meant that some customers were unable to login into the system.
This issue was rectified earlier today.

Internet banking was also affected and customers were unable to login to the site until later this afternoon.

"Internet Banking is up-and-running but some customers may find it slower than normal, given the high number of people logging-in right now," the bank said in a tweet at 1630 AEDT.

NAB said the internet banking blackout was unrelated to the system issues which struck the bank last year.

"There are no security issues or issues with transactions. The issues were related to the capacity of people to access the service," bank spokesman George Wright said.

The bank apologised for any inconvenience this may have caused.