SYDNEY, Oct. 18 (Xinhua) -- Australian financial giant, the Commonwealth Bank, has issued an apology to its millions of customers on Friday after a nationwide outage on Thursday that left account holders unable to access their own money.

(File photo: AFP)

"We are very sorry for the inconvenience this is causing our customers. We want to assure customers that their accounts are safe," the country's largest bank said in a statement.

"We have been working to restore the network systems overnight and these are now returning to normal."

"Some payments may be delayed appearing in accounts. We are working through the backlog as quickly as possible, but rest assured all payments both into and out of customer accounts will be properly processed."

Blaming Thursday's blackout on a systems upgrade failure, the Commonwealth Bank added that extra staff have been put on to deal with the logjam of payments and enquiries.

But despite the apology, furious customers took to social media to vent their frustration.

One person wrote, "Just wondering what compensation you are planning to give ALL customers in relation to this outage? Completely unacceptable. I now have had no food since yesterday, no petrol and now no money for the weekend and my daughter. There would be far worse than my situation."

Another Twitter user said, "Some services were still down. 13-hour outage, what a disgrace."

As of 12:25 p.m. AEDT on Friday, the price of Commonwealth Bank's stock had fallen 0.97 percent to 79.38 Australian dollars (54.23 U.S. dollars) per share.