The Singapore-flagged tanker, a 260,000-tonne single-hull crude carrier, was transporting about 250,000 tonnes of crude oil from Mina al Fahal port in Oman and Ras Tanura in Saudi Arabia, Mitsui O.S.K. said in a statement.

It was rescuing crew members from a cargo vessel that had caught fire and its oil tanks were damaged when the two ships came into contact.

Mitsui said the spill had been contained and there was no risk of further leaks. The impact on the environment should be limited because the spill occurred far from land, it said.

There was no plan for any cleanup as the oil should disperse naturally in the sea, the company said.

Indian Coast Guard ships were on alert but officials said since the spill was outside India's exclusive economic zone they did not expect any environmental fallout in the country's waters.

"We hope the oil will churn and disintegrate in the high seas, but we are watching closely," S.P. Sharma, a senior Indian Coast Guard officer, told Reuters by phone from Port Blair, the capital of the archipelago of Andaman and Nicobar.

Great Nicobar is the southernmost of the island chain.

A Mitsui spokesman said the tanker's engine was undamaged and it was continuing eastward with the remaining crude.

The spokesman said the tanker would stop at a port for repairs to its damaged tanks, though he did not know where it would stop or how long the repairs would take.

The buyer of the crude oil was Cosmo Oil Co., Japan's fourth-largest oil refiner, and the tanker had been scheduled to deliver it to Chiba, near Tokyo.