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 explosion 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 didn't give any details on how many had died.