An intensifying cyclone churned north towards Bangladesh on Monday after heavy rain in Sri Lanka and thunderstorms in eastern India killed over 200, with more torrential downpours forecast.
Bangladesh, hit by cyclones every year, warned that some low-lying coastal areas were "likely to be inundated by a storm surge of four to five feet (1.2 to 1.5 metres)" above normal and raised the storm danger signal to seven on a scale of one to 10.
Cyclone Mora was expected to make landfall on Tuesday morning.
Devastation in Sri Lanka
Authorities say floods and landslides in tropical Sri Lanka, off India's southern tip, have killed at least 177 people in recent days.
The officials said floods have reached roof level and cut off access to many rural Sri Lankan villages, disrupting life for half a million people, many of them workers on rubber plantations.
Villagers in Agalawatte, in a key rubber-growing area 74 kilometres (46 miles) southeast of the capital, Colombo, said they were losing hope of water levels falling soon.
Fifty-three villagers were killed and 58 were missing.
"All access to our village is cut off. A landslide took place inside the village and several houses are buried," said Mohomed Abdulla, a resident.
Rescue teams are using helicopters and boats to reach isolated areas. Following the government's call for help, international aid has started to arrive.
Bangladesh, India brace for impact
Authorities in Bangladesh say they will relocate thousands from coastal areas as Cyclone Mora bears down.
About 10 million of Bangladesh's population of 160 million live in low-lying coastal areas.
"We have taken all sorts of steps to minimise any losses, including moving people away from the most vulnerable areas," Kazi Adbur Rahman, a senior government official in Cox's Bazar.
Meanwhile, India too has warned of heavy rains in the northeastern states of Tripura, Mizoram, Manipur, Nagaland and Arunachal Pradesh as Cyclone Mora moves further up the Bay of Bengal.
Twenty-four storm-related fatalities have already been reported in the eastern Indian state of Bihar.