SAHARSA, India: Hundreds of thousands of flood victims huddled into makeshift camps in India and Nepal face major disease outbreaks if help fails to reach them quickly, aid workers warned Tuesday.

They said several camps in India's northern Bihar state and across the border in Nepal, areas devastated when a monsoon-swollen river which burst its banks and changed course, were already reporting cases of diarrhoea and other crippling illnesses.

A large part of Bihar is under water, and 550,000 people have been displaced. An estimated 400,000 people also still need to be rescued, state officials said.

At least 60,000 people have also had their homes washed away in southern Nepal.

"It's normal when there are a lot of people to have some cases, but when you have a number of cases, it becomes a concern and we have to do active surveillance," UNICEF emergency specialist Mukesh Puri told AFP.

In many areas, the wells have been inundated with flood waters containing sewage, bodies and refuse.

"There are no facilities apart from food," said Malini Morzaria of the European Commission's humanitarian aid organisation (ECHO), which is also working in the disaster area.

"The important thing now is for there to be some camp management, where the people have access to latrines, clean drinking water and some basic health care."

The relief operation in Bihar, however, is proving slow going - and dangerous.

Most people reaching safety in Saharsa, some 150 kilometres (95 miles) east of the state capital Patna, are traumatised by the loss of their homes, crops or loved ones, and carry few or no possessions.

At least 15 people drowned overnight in two separate accidents involving overcrowded rescue boats involved in the effort to ferry stranded villagers to safety, Bihar state disaster official Pratyay Amrit told AFP.

The dead included many children who were washed away by the strong currents still gushing through Supaul and Madhepura districts, two of the worst affected areas.

"These were areas that rescue teams had been struggling to reach and evacuate people," Amrit said.

At least 100 people have been confirmed dead since the Kosi river smashed through flood defences in Nepal and shifted course two weeks ago. The real toll is believed to be far higher as many people were simply washed away by strong currents.

Lieutenant-General H.S. Panag, the Indian army official coordinating relief work, said the floods were "the biggest national calamity in recent times."

Bihar state's chief minister, Nitish Kumar, suggested the humanitarian crisis was likely to be extremely serious for several weeks.

"The possibility of water receding is minimum until next month," he said.

The northern and northeastern states of Uttar Pradesh, West Bengal and Assam have also been badly hit.

Impoverished Nepal is meanwhile struggling to rebuild flood defences, and also cope with tens of thousands of homeless.

"At least six displaced people have died already from various diseases in the camps," said Durga Bhandari, the chief local official in Sunsari district, where most of the 60,000 displaced people in Nepal are staying.

"People have started suffering from fever, pneumonia and diarrhoea," added said Sanjeev Kafle of the Nepal Red Cross. "We fear there is a high chance of outbreaks of diseases like cholera and Japanese encephalitis."

- AFP/yt