The incident occurred around 12.30 PM when a group of 10-12 masked men entered the unit and threatened the workers with knives, said DCP (South Zone)VSatyanarayana.
He said the men tied up 21 workers before fleeing with the gold.
"Around 5 kg of gold was robbed. They also took away the CCTV cameras installed in the unit," the officer said.
He said the police are suspecting involvement of some former and current employees. "We have got some clues," he added.
Police have formed special teams to trace the accused.