The seven missing are staffers of Mumbai-based firm Adsun Offshore Diving Contractors Pvt Ltd, a company official said requesting anonymity.
According to reports received by the company, the divers and electrician were working on the Iranian diving support vessel when it suddenly sank around 5 p.m. Thursday.
The vessel is believed to have sunk more than 200 feet underwater with limited oxygen supplies.
Top company officials have rushed to Iran to monitor the situation, the official said.
She declined to reveal the identities of the victims until further updates on their status was made available to the company.