The unit, owned by one Dharambhai Patel, is located in Kumudwadi area of the city, according to police.
Anil Makwana (27) and Chandu Kumbhani (28), who were sleeping in the unit, apparently confronted the robbers after spotting them late last night, said a police official.
He said the duo had injuries caused by sharp weapons on their necks.
The incident came to light this morning when the caretaker of the unit spotted bodies of the two workers and alerted police.
Police found polished and unpolished diamonds worth over Rs 3 lakh stolen, the official said.
A case of murder and loot under respective sections of the IPC was registered at Bhavnagar B Division police station and investigation is on, he added.
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