I will add as concrete information becomes available.
A submarine reportedly exploded and caught fire subsequently sinking at the dock. There may be as many as eighteen sailors trapped in the submarine.
The link has a photo of a large fire line.
It is unknown if this submarine is a diesel over electric or nuclearly propelled. The Indian Navy only has diesel over electric submarines in their fleet. It is also unknown if there were and weapons on board at this time and what their composition might be.
The blast happened on the INS Sindhurakshak around midnight and was shortly followed by a massive fire. Many of the sailors on board the submarine reportedly managed to jump off to safety, but more than a dozen are feared trapped inside the hull.
INS Sindhurakshak (S63) is a Sindhughosh-class diesel-electric submarine of the Indian Navy.
On 4 June 2010 the Indian Defence Ministry and Zvezdochka shipyard signed a direct contract to the upgrade programme, worth $80 million and including a complete overhaul including the submarine’s hull structures.
In August 2010, INS Sindhurakshak arrived at Zvezdochka shipyard in Russia, for an overhaul and upgrade.
INS Sindhurakshak was retrofitted in Russia under Project 08773 in Zvezdochka shipyard. The submarine has been modernized and repaired and its sea trials started earlier in October 2012. The upgrade includes improved electronic warfare systems,control systems, and integrated weapon control system. This modernization enables incorporation of new Russian missile system Club-S with 200-km cruise missile range, Indian sonar USHUS and radio communication systems CCS-MK. There is a possibility to incorporate the Indian-built BrahMos cruise missiles later.
The optimal crew level is fifty two sailors and officers. This submarine suffered a fire in the battery compartment in 2010.
The fire has been brought under control.
The fire has now been brought under control but the vessel is partly submerged at its berth. Rescue workers are at the scene.
The Indian government has already formed a board of inquiry
H/T to Morgan Sandlin: Video