Dhaka - Many low-lying coastal districts and offshore islands on the Bay of Bengal have gone underwater as cyclone Aila heads toward Bangladesh, officials and local residents said Monday.

Bangladesh's Meteorological Department has asked its maritime ports to hoist danger signal number seven. The highest danger signal is number 10.

The department forecast that low-lying areas of at least 15 administrative districts and major islands in the bay are likely to be inundated by wind-driven surges between one and two meters above normal tide.

But local residents said that water surges have washed away many coastal homes as the cyclonic storm Aila, over the northern bay and adjoining west-central bay, moved northwards.

"People have rushed to cyclone shelters as their homes washed away," said Nasir Uddin, a resident of Patharghata sub-district, which was devastated by the 2007 super cyclone Sidr, on the Bay of Bengal.

The cyclone was centred about 435 kilometres south-west of Chittagong port, 405 kilometres south-west of the tourist city of Cox's Bazar port and 285 kilometres of south-southwest of Mongla port at 9 am local time (3000 GMT).

The storm was likely to intensify further and move in a northerly direction. It may cross the coast of the Indian State of West Bengal and Bangladesh's Khulna division by Monday evening.

Maximum sustained wind speed within 54 kilometres of the storm centre is about 70 kilometres per hour, rising to 90 kilometres per hour in gusts.

The chief administrator of southern Barguna district, Sawpan Kumar Sarker, said that his costal town has gone under water because of the cyclone.

All fishing boats and trawlers in the northern bay have been advised to remain in shelter until further notice.(dpa)