Millions of Australians were left unable to access their bank accounts or use debit and credit cards for more than four hours on Monday.

The nation’s largest bank, the Commonwealth Bank, reported a nationwide outage had affected its app and internet banking from about 10.30am (AEST).

At 1pm, the outage was still affecting customers across the country who were unable to buy groceries and fuel.

It wasn’t until 2.25pm on Monday Commbank announced on Twitter that its services had returned.

Earlier, customers complained their accounts weren’t showing on internet banking, while others said cards had been declined while shopping online.

Commonwealth Bank confirmed it was aware of the problem.

But it was not until 1.30pm that it said it was “starting to see services resume”, and another hour before the issue was apparently resolved.

“I’m trying to place an order and I can’t even see how much is in my account. Grrrrr, I can’t even see when the last transaction was made! I’m thinking of leaving,” customer Kat Cetwerschuk wrote on the CBA’s Facebook page.

“All you have to do is go & see the friendly staff at your local branch. Oh wait, they closed the branch & took away your ATM,” wrote John Staker.

Other customers reported their cards being charged twice or being rejected.

Bank staff advised customers to insert their cards and use PINs where possible, rather than payWave.

Tweet from @CommBank