More than 600 National Australia Bank branches across the country have shut their doors over a "physical security threat".
The bank announced about 2pm on Wednesday that it had closed all of its branches.
NAB later confirmed that included co-located commercial offices.
ATMs within branches have also been taken offline.
"As always the safety and security of our customers and colleagues is our priority," NAB said in a statement.
"We are progressively sweeping our branches, business banking centres and commercial offices to ensure they are safe to return."
When deemed safe, the bank said workers would be advised they can return and the branches reopened to customers.
"We are working closely with police and will provide an update as soon as we can," it said.
NAB said digital banking via internet, mobile and telephone services was unaffected and remained online.
The lender has more than 600 branches across Australia and there is no indication of a time frame for when they will reopen.
