(CNN) -- The United Nations is warning of a massive "health crisis" in southern Asia, where 30 million people have been overwhelmed by the monsoonal rains and flash flooding sweeping across India, Nepal and Bangladesh.
"Entire villages are days away from a health crisis if people are not reached in the coming days," said Dr. Marzio Babille, the U.N. Children's Fund health chief in India.
His remarks were made in a statement issued by the agency, also known as UNICEF.
Such weather is an annual event, but this year it is particularly intense and it is a challenge for relief workers to reach the millions of displaced and marooned.
The affected area is in India's Assam state in the country's northeast and Bihar and Uttar Pradesh states in the north and in Bangladesh and Nepal -- which border this stretch of India.
The rains and floods have inundated the infrastructure, the water has become contaminated, and death tolls range in the hundreds.
Structures across the region -- such as dwellings, schools and hospitals -- "have been either damaged or lost."
In the Tuesday statement, UNICEF's Babile said that "many of the affected areas are home to poor communities who suffer from poor sanitation and hygiene year round.
"Stagnant waters left by the floods are a lethal breeding ground for diarrheal and waterborne diseases at potential epidemic level, skin infections and other public health threats such as malaria, leptospirosis and dengue fever. Children, who make up 40 per cent of South Asia's population, are particularly susceptible."
One U.N. official, Nick Nuttall, U.N. Environment Program spokesman, told CNN last week that it appears the intense weather is the "signature of climate change" and the heavy toll is related to various societal trends over the years.
These include population growth and an increasing number of people dwelling in marginal areas, such as flood plains and mountainsides; deforestation; and the draining and loss of wetlands.
"If you add all these kinds of factors, human vulnerability is more extreme" now than it was decades ago, Nuttall said. E-mail to a friend