DIG (Saran range) Vinod Kumar said over a dozen motorcycle-borne robbers stopped the cash van at gun point near Hansrajpur village and shot at and injured two security guards of the van.
They then looted Rs 1.20 crore and fled from the spot, about 25 kms from the district headquarters.
The van was carrying cash from the bank's main branch at Chapra to its Janata Bazar branch in the district, Kumar said.
Roads in nearby areas were sealed and raids were being carried out to nab the robbers and recover the cash, he said.