National Australia Bank (ASX: NAB) has suffered an outage of its internet and telephone banking systems today, only two months after a computer system glitch delayed the processing of payments and transactions of thousands of customers.

“NAB internet banking is currently experiencing technical difficulties,” the internet banking website said.

“We are investigating the cause of the interruption and will restore the service as quickly as possible.”

The bank also posted messages to Twitter that it was "working to resolve the issue" that began approximately 11am.

NAB's website crash came a day after UBank, a division of NAB, experienced a separate glitch.

"Our apologies to UBank customers who received duplicate emails & SMS, we are currently experiencing issues & are looking into it now," the bank reported yesterday.

Late November last year, NAB experienced a major IT outage resulting in payments made overnight not appearing in potentially "millions" of customers' accounts.

All types of payments had been disrupted by the four-hour systems outage, including NAB EFTPOS, ATM and other electronic banking facilities.

Shares in NAB have slipped 0.74 per cent and are trading at $24.26 at noon.