Three masked men armed with semi-automatic guns walked into the Bank South Pacific BSP branch, in Auki, Malaita and robbed the bank.
They then hijacked a truck and took off with bags of money.
Police are now questioning witnesses who were there.
Hundreds of people were at the bank waiting to withdraw their salaries when the robbery happened.
The bank is yet to confirm how much was stolen.
The police commissioner, Frank Prendergast, says the situation is fluid.
