At least 38 more people died overnight in Bangladesh, including two from water-borne diseases, raising the death toll in the low-lying country's worst floods in recent years to nearly 500, officials said on Wednesday.

The flood waters that have also inundated large parts of eastern India have since receded, but millions remain homeless and vulnerable to disease, aid officials said.

More than 53,000 people have contracted diarrhoea in Bangladesh, mostly caused by eating stale food and drinking impure water. A field hospital has been opened in the capital, Dhaka, to treat diarrhoea patients.

"The overall diarrhoea situation is grim. Everyday there is a rush of patients," said Ayesha Khatoon, a senior official at the government's health directorate. "We are trying to cope with it."

One doctor at the Dhaka-based International Centre for Diarrhoeal Diseases Research said the facility had received 1,100 patients on Tuesday, the highest single-day admissions in its history. "We suspect the flow will increase further," said Doctor Azharul Islam Khan.

The country's interim government said it was doing everything possible to ensure that flood victims get food, clean water and access to healthcare.

With floods easing, many people in relief camps are heading back back to their homes. "They hardly have a roof on their heads or anything to eat," said an official in northern Kurigram district, one of the areas worst hit by the floods.