Millions left homeless by Asia's monsoon floods

Death toll could hit thousands as abnormal rain swamps Bangladesh, Nepal and northern India, bringing threat of mass starvation and waterborne disease

Women and children were seen screaming for help from treetops yesterday as monsoon floods struck three countries in south Asia, leaving at least 280 people dead and 20 million washed out of their homes.

Abnormal weather in northern India, Bangladesh and Nepal has caused river levels to rise by 30ft in some areas, flooding surrounding areas so fast that many people were unable to save even the most basic possessions. Confirmed deaths have reached 54 in Bangladesh, 84 in Nepal and 148 in India, but it is feared the toll could climb to thousands as the threat of starvation and water-borne diseases increases.

The floods are already the worst to hit the region in 30 years, and more heavy rain is forecast this week. Thousands of villages and rice paddies are submerged at the peak of the rice-planting season, and it is feared that crops could be permanently damaged, leaving millions destitute. Food supplies are already running low.

Helicopters dropped food to nearly two million villagers yesterday in the badly hit state of Uttar Pradesh. Assam and Bihar are the other worst-affected states in India, where it has been raining heavily for three weeks. There were reports of clashes between police and flood victims in several relief camps in Assam, where aid efforts have been severely hampered by the collapse of more than 60 bridges.

The police, the military and hundreds of volunteers have been mobilised by all three governments to help evacuate people and distribute food and medical aid. But the sheer scale of the disaster poses an unprecedented challenge, according to the United Nations children's fund, Unicef.

In Nepal, floodwaters have started to recede and the clean-up operation is under way, but around 300,000 people have been displaced and the threat of diseases such as diarrhoea, typhoid and cholera remains high.

In Bangladesh, two-thirds of the country has been affected, with parts of the capital, Dhaka, still under water. Almost seven million Bangladeshis are either displaced or isolated in villages, but the government insisted it was coping, despite aid efforts being slowed by a lack of boats.

India's meteorological office said "unusual monsoon patterns" had led to heavier than normal rains this year. More than 1,100 people have already died since the rains began in June. India's financial capital, Mumbai, on the opposite coast, was knee-deep in water this weekend, disrupting transport, schools and businesses. But the annual rains brought in by south-westerly winds are always dangerous – last year more than 1,000 people died, most from drowning, landslides or house collapses.

"Unknown numbers of people are either stranded or have been displaced and lack any form of shelter," said Unicef. "They have lost their homes, possessions, livestock and fields and will have to begin their lives again from scratch." Save the Children has launched an appeal amid warnings of food and medicine shortages.