Millions of villagers hit by monsoon floods across northern India, Bangladesh and Nepal are ''days away from a health crisis,'' as stagnant waters become a breeding ground for disease, the United Nations said.

About 30 million people have lost their homes or livelihoods after monsoon rains and melting Himalayan snow caused rivers to burst their banks, the UN Children's Fund, Unicef, said in a statement yesterday.

Floodwaters ''are a lethal breeding ground for diarrheal and waterborne diseases at potentially epidemic levels,'' Marzio Babille, Unicef's health chief in India, said in the statement, adding malaria and dengue fever are among the threats. ''Children, who make up 40 percent of South Asia's population, are particularly susceptible.''

Monsoon rains between June and September are essential for agriculture in South Asia and cause annual flooding. This year's monsoon rains have been of a ''startling magnitude and intensity'' and caused the region's worst floods in living memory, Unicef said.

Almost 20 million people have been affected in the Indian states of Assam, Bihar and Uttar Pradesh, the agency said. Hundreds of thousands of people are camping on highways, railway tracks and rooftops to escape the floods, many without clean drinking water.

Danger Levels

In Bangladesh, a low-lying delta nation, 8 million people have been affected, according to the statement. Twenty-six rivers are flowing above danger levels and 1.2 million acres (485,000 hectares) of cropland have been damaged. Diarrhea, cholera and skin diseases are spreading.

Flooding across Nepal has affected more than 300,000 people, mostly in rural areas of the Terai along the southern border with India, Unicef said.

The death toll in India stands at more than 1,000, Unicef said Aug. 3. In Nepal, floods, landslides and disease have killed 95 people, the agency said yesterday. In Bangladesh, more than 100 have died, according to disaster management officials.

UN Secretary-General Ban Ki-moon is ''deeply saddened by the hundreds of lives lost'' and ''concerned by the economic devastation faced by the survivors,'' his office said in a statement yesterday.