Commonwealth Bank users are reporting an error which has seen duplicate transactions being taken out their bank accounts, resulting in overdrawn accounts for some customers.
The bank said the process to reverse the transactions was now complete.
"We have resolved an earlier issue where some customers experienced duplicate transactions in their accounts. The process to reverse these transactions has been completed," a spokesperson said.
"Please be assured any fees charged will be refunded. Customers do not need to contact us to request this."
At around 5:40pm AEDT, CommBank tweeted that the process to reverse the "duplicate transactions" has been completed.
"We apologise to customers who had transactions duplicated in their accounts today," the statement said.
The statement added that customers are now seeing the "duplicate transactions" disappear.
A spokesperson for Commonwealth Bank said people who are finding themselves in financial difficulty can call 13 2221 or visit a branch for potential support such as a temporary overdraft.
Melbourne man Tom Kelly first noticed the error when he tried to buy a coffee at work on Saturday morning and found his account was overdrawn by more than $100.
He had no communication from the bank and said he initially "couldn't work out what was going on".
Hours later, he said he had been put on hold for 40 minutes and couldn't access the bank's online chatbot Ceba.
As of 5:30pm AEDT, the digital assistant appears to be up and running for some customers.
"I'm worried I won't be able to get an Uber home from work," Mr Kelly said, noting public transport added a significant time to his commute home.
"[Even then] I've got to make sure I have enough to tap on."
Mr Kelly said he had filed a complaint with the Australian Financial Complaints Authority.
"It's unbelievable," he said.
"We're not all rich and well-off.
"There's some people out there where those transactions are the last dollar for the week."
User Chris told ABC Radio Melbourne his account was also overdrawn by "the hundreds".
He said he has had "no communication or acknowledgement" from the bank's end.
"Acknowledgement would have been great from the start, but then what are the next steps would have been great," he said.
Chris said the error had put his weekend in disarray, including a first birthday party he was planning.
"We're just trying to figure out if we can use our card," he said.
"Ok yeah we can move money from our savings for spending but is that going to be overcharged?
"There's a lot of expenses involved, in terms of catering, so you know if you're spending $500 is it $1,000?
"You don't have that confidence in going to the shops."
One customer on social media said they had been at the pharmacy to buy medication when they noted five duplicate transactions.
It comes as Westpac and subsidiaries including St George, Bank of Melbourne and BankSA were hit by a string of outages last week that saw customers experience difficulties accessing internet banking for three days.