At 2 AM today, about six dacoits broke into the shop in Mohiuddnagar market, said Deputy superintendent of police Rajendra Prasad.
The jeweller and his family, who live in the same building, rushed to the shop on hearing the commotion but the dacoits held them hostage and forcibly took the keys of the locker from them, police added.
They then decamped with the ornaments and cash kept in the locker.
Police are investigating into the incident and raids are on to nab the culprits.