The blast was heard ashore by Deputy Chief Fire Officer P.S. Rahandale who was on leave and attending a private engagement near the Gateway of India promenade.
He immediately alerted his superiors as well as the Fire Brigade and other emergency services to rush to the scene of the tragedy and immediately render assistance.
"When I heard the huge explosion on the promenade, I realized that this was something major and I started for the disaster site. When I reached there, the scene was one of utter devastation," Rahandale told IANS at 3 a.m. Wednesday.
Tall flames were leaping from the newly refurbished and armed INS Sindhurakshak, making it difficult for the rescue teams to even venture close to the spot to render assistance and battle the conflagration, he said.
At that time, he noticed another submarine berthed barely five-six metres away from INS Sindhurakshak which was breathing fire in all directions.
Realising the danger from the leaping flames, Rahandale alerted his fire-figthers and those from the Indian Navy and Mumbai Port Trust to make attempts and save the neighbouring submarine.
"From the fire tenders, we built a wall of water-jets between INS Sindhurakshak and the other vessel nearby, thereby giving a safe window to sail it to a safe distance," Rahandale said.
Though the fire on INS Sindhurakshak was brought under control and prevented from spreading or damaging other naval fixed and floating assets in the vicinity, the vessel sank in the shallow waters around dawn Wednesday.
There are concerns about at least 18 sailors who were aboard the vessel.
A team of Indian Navy divers has been deployed since morning in an effort to rescue some of their colleagues feared trapped inside the sunk vessel.
Chief of Naval Staff Admiral D.K. Joshi will take stock of the situation even as a Board of Inquiry has been ordered into the incident.
Shortly after midnight, a huge explosion accompanied by a fire rocked INS Sindhurakshak which was docked in the high security Naval dockyard early Wednesday.
Many sailors on board the submarine reportedly jumped off to safety.
The cause of the explosion and blaze, as well as the extent of damage to the submarine and naval properties, is still not known.
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