New Delhi ( CNN ) -- An unspecified number of Indian sailors have died after an explosion and fire on a navy submarine at a dockyard in Mumbai , authorities said Wednesday . Rescue efforts are under way at the scene following the blast and `` major fire '' early Wednesday on the INS Sindhurakshak , the defense ministry said in a statement . Defense Minister A.K . Antony later said that some officers had lost their lives , but he did n't give any details on how many had died . The Russian-built submarine has mostly sunk from the damage , the defense ministry said , and only a part of it is visible . About 18 people were on board the vessel at the time of the blast , it said . Images carried by CNN sister network IBN showed the night sky over the port area lighted up by the explosion and blaze , which began shortly after midnight . Navy and civilian firefighters were called into action at Mumbai 's naval dockyard to tackle the flames and rescue survivors . By Wednesday afternoon , the navy had taken sole responsibility for the rescue effort , Mumbai fire chief Suhas Joshi said . An inquiry has been ordered to determine the cause of the explosion , the defense ministry said . In 2011 : Probe , repairs ordered after Russian nuclear submarine fire . Refitted in Russia . The Sindhurakshak was commissioned in 1997 , according to the Indian Navy . It was refitted in a Russian shipyard between August 2010 and January of this year , Russian state new agency Itar Tass reported . The redesign included the installation of new missile , communication and cooling systems , as well as a new radar , the agency said . It reported that the upgrade also included other measures to improve the submarine 's combat quality and operational safety . The crisis at the Mumbai dockyard Wednesday comes after India launched a home-built aircraft carrier Monday in a bid to join a select group of nations capable of building such warships . In 2012 : Vacuum cleaner blamed for fire on nuclear submarine . CNN 's Harmeet Shah Singh reported from New Delhi , and Jethro Mullen wrote from Hong Kong . Joseph Netto in Atlanta contributed to this report .
Russia : The defense minister confirms some deaths but does n't say how many . About 18 people were reportedly on board when the blast happened . Rescue efforts are still under way . The Russian - built submarine has mostly sunk following the explosion and fire .