A government doctor in Bangladesh warned that the southern part of the country was on the brink of an acute diarrhoea outbreak, days after a cyclone hit the region and neighbouring India.
At least 219 people were killed after Cyclone Aila on Monday slammed into the coast north of the Bay of Bengal, where a large-scale military and civilian relief operation is under way.
"There's an acute shortage of drinking water and as a result diarrhoea has broken out," Lutsur Rahman Khan, medical chief of Bangladesh's Khulna district, told AFP.
"The situation is bad and it's a race against time to prevent a full-scale epidemic from breaking out."
Khan said several levees had been washed away by the cyclone, particularly in Dakope and Koyra close to the Indian border, meaning areas were being flooded during high tides.
Drinking water is in short supply and the salty water could not be treated with purification tablets, he said, adding that water-treatment facilities brought in by the army were also unable to purify sea water.
Some 149 people died in Bangladesh -- where more than 500,000 people's homes were damaged or destroyed -- while 70 more people were killed in India following Monday's cyclone.
About 20 of those killed in West Bengal in India died a day after the storm in mudslides caused by rainfall in the hill resort of Darjeeling.
The low-lying region frequently experiences tropical storms and cyclones during the monsoon season.
In 2007, more than 3,500 people were killed, most of them in Bangladesh, when Cyclone Sidr hit the same districts.