It is unclear what caused the explosion on the INS Sindhurakshak.

According to India media reports many sailors jumped to safety and some of the injured were taken to hospital. Firefighters and rescue workers are at the scene.

Smoke from the blaze could be seen in many parts of the city, reports said.

"There are some people who are trapped on board, we are in the process of trying to rescue them, we suspect it to be in the range of 18," Navy spokesman PVS Satish was quoted by the Reuters news agency as saying.

"We will not give up until we get to them," he added.

The 16-year-old Russian-made vessel had recently returned from Russia after undergoing an upgrade, the AP news agency reports.