A tiny island claimed for nearly 30 years by India and Bangladesh in the Bay of Bengal has disappeared beneath the rising seas, scientists in India say.

The uninhabited territory south of the Hariabhanga river was known as New Moore Island to the Indians and South Talpatti Island to the Bangladeshis.

Its disappearance has been confirmed by satellite imagery and sea patrols, the School of Oceanographic Studies in Calcutta said.

New Moore Island in the Sunderbans has been completely submerged, Sugata Hazra, oceanographer and professor of the School of Oceanographic Studies at Jadavpur University in Calcutta, said.

"What these two countries could not achieve from years of talking, has been resolved by global warming," he said.

Anyone wishing to visit now, he observed, would have to think of travelling by submarine.

Rising sea levels

Scientists at the School of Oceanographic Studies at the university have noted an alarming increase in the rate at which sea levels have risen over the past decade in the Bay of Bengal.

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Until 2000, the sea levels rose about 3 millimetres (0.12 inches) a year, but over the last decade they have been rising about 5 millimetres (0.2 inches) annually, Hazra said.

Another nearby island, Lohachara, was submerged in 1996, forcing its inhabitants to move to the mainland, while almost half the land of Ghoramara island was underwater, he said.

At least 10 other islands in the area were at risk as well, Hazra said.

"We will have ever larger numbers of people displaced from the Sunderbans as more island areas come under water," he said.

Bangladesh, a low-lying delta nation of 150 million people, is one of the countries worst-affected by global warming.

Officials estimate 18 per cent of Bangladesh's coastal area will be underwater and 20 million people will be displaced if sea levels rise one metre by 2050 as projected by some climate models.

India and Bangladesh both claimed the empty New Moore Island, which is about 3.5 kilometres long and three kilometres wide.

There were no permanent structures on New Moore, but India sent some paramilitary soldiers to its shores in 1981 to hoist its national flag.

The demarcation of the maritime boundary - and who controls the remaining islands - remains an open issue between the two South Asian neighbours, despite the disappearance of New Moore, said an official in India's foreign ministry, who spoke on condition of anonymity.