DHAKA, Sept 23 (Reuters) - More than 100 Bangladeshi fishermen were missing after at least 15 fishing boats sank in a storm in the Bay of Bengal, witnesses and officials said on Sunday.

The Chittagong port authority issued an international maritime alert advising all ships and fishing boats to remain in shelter until further notice, said Syed Farhad Uddin, the secretary of the Chittagong port.

Bangladesh's meteorological department said in a special weather bulletin that the monsoon deep depression, which hit the Bay of Bengal on Thursday night, was moving north-north-west and had reached India's eastern coastal state of Orissa.

"Maritime ports of Chittagong, Cox's Bazar and Mongla have been advised to keep the local warning signal hoisted," the bulletin said.

Heavy seas were preventing rescue operations, but authorities said they would start a search as soon as the stormy weather subsided.

Surviving fishermen said that they saw several boats to sink. In Cox's Bazar, about 10 fishing boats with nearly 100 fishermen capsized, but about 80 fishermen made it back to shore.

Officials also warned of flooding, with low-lying areas of the several coastal districts, including Chittagong, Cox's Bazar and their offshore islands, likely to be inundated by water surges up to 4 feet (1.2 metres) high, driven by high winds.

Hundreds of Bangladeshi fishermen die and many go missing in storms in the Bay of Bengal every year. (Additional reporting by Nazimuddin Shyamol in Chittagong and Nurul Islam in Cox's Bazar)

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