Fears are rising for hundreds of villages stranded by flood waters in large areas of Nepal, Bangladesh and India.

"This is the worst flooding that parts of South Asia have seen in decades. Entire communities have been cut off. The only way to get aid to some of these villages is by boat and many are running out of food," said Jagan Chapagain, Under-Secretary General for Programmes and Operations, International Federation of Red Cross and Red Crescent Societies, IFRC.

"The situation is going from bad to worse. In Nepal, as waters finally recede, our teams are finding communities that have lost homes, identity documents – everything. In Bangladesh and India, the number of people affected is rising by the hour as waters rush south," he added.

Overall, more than 24 million people are believed to be affected by flooding in the three countries, with more than 700 people thought dead. Some 1,800 Red Cross and Red Crescent volunteers are working alongside local authorities to prevent further deaths and help communities withstand and recover from the floods.

Clean water and sanitation are major priorities in each of the affected countries with increasing incidents of diseases already being reported.

"The floodwaters have become a breeding ground for deadly diseases such as diarrhoea and malaria. We fear that other diseases such as dengue and Japanese encephalitis are also on the rise," Chapagain said.

In low-lying Bangladesh, the Red Crescent has described the flooding as some of the worst the country has ever seen.

"Floodwaters are sweeping from the north of Bangladesh to the centre, submerging whole villages. Many communities are isolated, with no access by land. Millions have been forced to camp on any patch of dry land they can find," said BMM Mozharul Huq, Secretary-General of the Bangladesh Red Crescent Society.

"We are delivering aid, food, water and other vital supplies but this disaster is one of the biggest we have ever faced. We are appealing for global support," Huq added.