New Delhi - Tens of thousands of cyclone survivors in India and Bangladesh desperately need clean water after the storm contaminated drinking sources with sea water, aid agencies say.

Relief workers also warned the death toll could soar if there are outbreaks of water-borne diseases following massive flooding.

Packing winds of up 100 kph, cyclone Aila slammed into eastern India and Bangladesh on Monday, killing at least 240 people and injuring over 6,500.

The storm whipped up 4-metre tidal surges which tore through embankments, sweeping away homes, ravaging crops and damaging roads and bridges.

About 4.6 million people in India's West Bengal state and around 3.7 million living along Bangladesh's coastal belt are estimated to have been affected.

Dozens are still missing, including a group of 16 children in India who were playing in an abandoned house which was washed away by a raging river in North 24 Parganas district in West Bengal.

As government officials and aid workers scramble to help, they say there is a dire shortage of clean drinking water because sea water has inundated hundreds of rivers, ponds and wells.

"The tidal waves and the upward flow of sea water into river deltas have deposited saline water contaminating all drinking water sources," said Dr P.V. Unnikrishnan, ActionAid's emergency coordinator for Asia.

"There is an urgent need to provide clean drinking water as well as clean up all the contaminated water sources."

In India, eight districts in West Bengal, including the city of Kolkata, were affected while in Bangladesh, 15 districts including Barisal, Satkhira, Barguna, Khulna and Patuakhali were seriously affected.

Some areas remain inaccessible as roads, railways and bridges have been damaged and aid workers fear hundreds of villagers are stranded with little assistance.

Disease Warning

Aid workers say thousands of people, who had sought refuge in cyclone shelters, schools and other buildings, are beginning to return home to find their houses destroyed, their fields submerged and their livestock dead.

"Families have lost their homes, livestock, crops, access to work and food and, in many cases, clean water and sanitation," said Ned Olney, vice president of Save the Children's global humanitarian response.

"We are working to get water treatment plants up and running so that a bad situation does not get much worse through the spread of disease."

There are fears of outbreaks of water-borne diseases in the coming days, followed by illnesses like malaria in the coming weeks.

"Hygiene risks are becoming a major issue as dead fish and livestock decompose - cholera, diarrhoea and skin infections are all expected to rise," said a situation report by Save the Children India.

Aid workers say engaging communities in helping to clean up water sources through cash-for-work programmes should be initiated now rather than as part of the early recovery phase.

They add that sanitary services such as building pit latrines, provision of basic sanitation items such as toilet paper and soap as well as public health education could help control the spread of diseases.

"We are fortunate that the number of deaths in this disaster is relatively less," said Unnikrishnan.

"But as has happening in the past, we could find more people dying from preventable diseases than from the direct impact of the disaster if we do not take action now."

Monsoons

The inundation of salt water has also destroyed paddy crops and rendered some agricultural land unusable.

While most villagers managed to harvest their rice paddy before the disaster, many had not sold their stocks, which were washed away in the floods.

Relief workers say the flood waters have also washed away seeds and destroyed stocks of freshwater fish and shrimp.

There are hopes that monsoons due in the coming weeks will flush out fields, ponds and rivers and also provide drinking water to affected communities.

"The monsoons will really help relief efforts as far as water issues are concerned as we can then get people to harvest the rain water, rather than dealing with trucking in water and supplying water purifications tablets," said Dr Babar Kabir, director of Bangladesh development organisation BRAC's disaster programme.

"Water is the immediate need but we will indeed have to look at long-term recovery for many people."