The Indian Coast Guard on Thursday launched search and rescue operations for the five missing crew members of an oil tanker that ran aground here on Wednesday, an official said even as shipping experts said they were perplexed at the sailors' decision to abandon ship.

"In the morning (Thursday) 15 crew members abroad Pratibha Cauvery were rescued by our two helicopters," a Coast Guard official said.

Anchored in Bay of Bengal near the Chennai Port, Pratibha Cauvery with 37 crew members started drifting towards the shore due to strong winds on Wednesday. Cyclone Nilam was set to cross the coast between Mamallapuram and Kalpakkam on Wednesday evening.

The ship ran aground on Wednesday afternoon at the Elliots Beach or Besant Nagar beach, following which 22 members of the tanker clambered into a life boat, said officials of Coast Guard and the Chennai Port Trust.

According to Coast Guard, the crew members embarked the ship despite their advice to the contrary.

Hit by giant waves, the boat capsized and five people went missing while 17 were rescued and admitted to a hospital, but one of them died.

"The condition of 14 were stable, two were critical but stable and one crew was declared dead due to drowning," a Coast Guard statement said.

According to Coast Guard, its ships Rani Abbakka, Raj Tarang, Priyadarshini and two Dornier aircraft have been tasked to augment the air/sea coordinated search operations.

Meanwhile an official of Pratibha Shipping that owns the oil tanker said the company would reward anybody who finds the missing crew a sum of Rs.100,000.

"We have asked our agent in Chennai to file a missing person complaint with the police. The vessel hull is in a perfect condition," an official of Pratibha Shipping said over phone from Mumbai.

He said the company has mounted search operations for the missing crew.

He said a Norwegian expert will be reaching Chennai to study the condition of the ship.

During the day, top officials of the shipping company had a meeting with the officials of Directorate General of Shipping.

For reasons yet not known, the 22 sailors decided to abandon the ship while the tanker's captain and others remained abroad.

Queried whether the sailors were not paid their dues, the shipping firm official said: "The priority is to rescue the missing crew. There might have been some minor dues. But the company is not a bad employer."

Shipping experts are perplexed at the decision of 22 sailors to abandon the ship as it is the safest place to be in and that too after the tanker was grounded.

"Basically the ship is always the safest place to be on any occasion. Even during the worst of fires and flooding, the ship is engineered to stay afloat and any trained crew, especially the captain, would know that abandon ship is an extreme-extreme case when the captain decides that jumping on to the sea is safer than staying on board.

"And I am not sure a cyclone is an extreme case at all. Sailors regularly encounter rough weather. An aground ship is not going to sink, unless the stern tube (the small tunnel that carries the propeller shaft) got damaged," a former sailor told IANS.

"Whether the ship was in a fit condition to sail in such a weather condition is the moot question. The Directorate General of Shipping has to come out with a statement," Manoj Joy, national coordinator for Sailors Helpline said.

He said it needs to be known whether the ship captain had kept the owners informed about the ship's condition.

Pratibha Shipping officials said they were waiting for a quote of dry docking the ship at the port outer after unloading oil at Chennai Port on late September.