About 700 diarrhoea patients a day are checking into an already overcrowded hospital in Dhaka as filthy flood waters spread disease across Bangladesh, health officials said on Friday.

"We are struggling to cope," said Prodip Bardhan, acting chief physician at the International Centre for Diarrhoeal Disease Research.

Tents have been set up to house extra patients, who are given bedpans and buckets to make up for the toilet shortage.

Devastating monsoon floods have swept across South Asia in the past few weeks, killing at least 600 people and destroying the homes of hundreds of thousands more.

The floods are slowly receding in many areas. Meantime, animal carcasses rot, sewage festers and mosquitoes breed in filthy water, spreading disease amongst exposed flood victims.

Across Bangladesh, two-thirds of which disappeared under flood waters in the last few weeks, about 100,000 people have caught dysentery or diarrhoea, officials say -- conditions that can kill patients if they do not have clean water to drink.

Pharmacists are hiking the prices of rehydration fluids, according to relatives of diarrhoea patients. Doctors at Dhaka's diarrhoea hospital said many patients were showing up malnourished, requiring extra treatment.

No one has died at the hospital since the outbreak, officials said, but 12 people have died from diarrhoea in rural districts of Bangladesh, according to reports. In Assam state, in northeastern India, stagnant flood water will take up to two weeks to drain, aid workers say.

On the other side of the country in Gujarat, floods have caused drain pipes full of sewage to split. Health workers are disinfecting worst-hit areas.

"The stench is everywhere. Diseases could spread like wildfire," said S. Singh, a state rescue official.

Aid workers in Bihar, one of the worst-affected states, say the number of people with diarrhoea has jumped dramatically in recent days.

Several families camping on the side of the road near Gaighat hamlet said their children were racked with fever but they had no medicine, and doctors were yet to visit.

Government and aid agencies were delivering sacks of food and clean water in helicopters and boats, but demand has mostly outstripped supply.

"With limited assistance from governments, and humanitarian agencies overstretched, help is still a distant reality for many," said P.V. Unnikrishnan of ActionAid in a statement.

"The response from the international community has been lukewarm. Time is running out -- money is running out."

But India denied needing help from outsiders.

"Even after the tsunami, which was a tragedy of much bigger dimensions, India helped other countries and did not ask for any aid," said Onkar Kedia, a home ministry spokesman, referring to the 2004 tsunami in the Indian Ocean.

"It's a big country and it can manage its own affairs."