The incident took place at Ramchandrapuram town.
The robbers entered the office soon after it opened at 10 am and showed a gold ring against which they said they wanted a loan. Then they forced the staff to open the locker at knife-point, said Deputy Superintendent of Police Surender Reddy.
"They locked the manager, the assistant manager and a woman sweeper inside the locker room, cut the wires of the CCTV cameras and took CCTV hard-disk containing footage of the incident before fleeing," the DSP said.