Millions of people affected by flooding in South Asia face a health crisis unless relief work is urgently stepped up, the United Nations has warned.

The World Health Organization (WHO) and UNICEF said stagnant waters were ""a lethal breeding ground"" for diseases such as malaria and dengue fever.
Food, drinking water and medicines are being distributed but the scale of the disaster has dwarfed relief efforts.
About 28 million have been affected by the floods in India, Bangladesh and Nepal.
""Entire villages are days away from a health crisis if people are not reached in the coming days,"" said UNICEF's health chief in India, Marzio Babille.
""Stagnant waters left by the floods are a lethal breeding ground for diarrhoeal and waterborne disease at potential epidemic level.""
Children, who make up 40% of South Asia's population, were particularly vulnerable, he said.
India is the worst affected country, with some 20 million people in the states of Assam, Bihar and Uttar Pradesh hit by the floods, according to the UN.
Some eight million people are affected in Bangladesh and another 300,000 people in southern Nepal, the UN said.
Although water levels are receding in Nepal and Bangladesh, millions of people are still marooned on high ground.
Most water sources in affected areas are said to be either contaminated or submerged.
Mr Babille told the BBC that an acute shortage of helicopters meant that the authorities in India were finding it difficult to reach victims, who have spent more than a week in the open, after their houses were either washed away or surrounded by water.
--------------------------- Fights and theft
There has been a brief pause in the rain but reports indicate more rain is on the way and the flood season is likely to continue for several weeks.
Indian Home Minister Shivraj Patil and Congress party head Sonia Gandhi visited the worst-hit region, in Bihar state, on Tuesday as anger rose over aid efforts.
About seven million people are affected in the state, and there have been reports of fights over limited supplies and of local officials stealing them.
The UN said that in Bihar alone, it needed many more helicopters for relief operations and at least one million more oral rehydration sachets to alleviate diarrhoea.
(Source: BBC