FNB says its Parktown branch will remain closed until further notice following a burglary on Saturday evening.
Hawks spokesperson Ndivhuwo Mulamu said an investigation team found two vaults were opened and R1.7-million in cash and valuables inside safety deposit boxes were stolen.
It is alleged that four unknown suspects gained entry by grinding through a wall of the bank.
The burglary follows one at an FNB branch in Randburg before Christmas.
Lee-Anne van Zyl, CEO of FNB Points of Presence, said at the moment there was no indication that the two incidents were related.
She said that affected customers would be notified individually.
FNB says it is working with the SAPS and the Organised Crimes Unit investigating the incidents.