PATNA, India : Helicopters on Sunday dropped food and other essentials to the millions of people forced from their homes by floods across South Asia, but officials warned that the aid efforts were insufficient.

The floods, triggered by unrelenting monsoon rains and glacial snow melt from the Himalayas, have inundated large swathes of India, Bangladesh and Nepal, leaving some 20 million people homeless or marooned.

At least 1,400 people have died since June in the worst flooding to hit the region in decades.

The Ganges, the Brahmaputra and dozens of other rivers have burst their banks, submerging thousands of villages.

In India's worst-hit state of Bihar alone, 11 million people - nearly 10 percent of the state's 120-million-strong population - have been affected by the disaster, leading aid officials to make a desperate plea for help.

"We have to do much more than what is being done," Job Zachariah, head of the hard-pressed Bihar chapter of the UN Children's Fund (UNICEF), told AFP as he coordinated relief efforts in the area.

"Two million are living on open embankments," he said.

Four helicopters dropped 11,000 emergency packets - each weighing five kilogrammes and packed with dry rations, candles, plastic sheets and match boxes - to those in need in Bihar, the Indian air force said.

But Zachariah warned: "It is just not sufficient. There is a need for a massive airlift to help people in 19 of Bihar's 38 districts."

State chief minister Nitish Kumar said he was deploying his senior aides to the worst-hit districts to speed up rescue and relief operations, as officials warned that water levels were still on the rise.

State monitoring teams meanwhile headed to India's border with Nepal to keep an close eye on water rushing down from the Himalayas into Bihar and neighbouring Uttar Pradesh state.

"If the discharges continue on this scale for another week, we could have a natural calamity unheard in the region's history," warned one senior official, who asked not to be named.

In Bihar's worst-hit district of Darbhanga, 5,000 desperate people stormed a former palace in search of food and much-needed shelter, aid workers said.

"Here we will not die of snake bites, diseases and hunger," said Akhilesh Yadav, a victim sheltering in the complex that is now an university campus.

In the village of Rajkhand Katonjha, hundreds sheltered on rooftops as the Bagmati River submerged their mud-thatched homes.

"We're offering prayers for dead as we don't know what will happen to us," said resident Sudhir Prasad, as children lay listlessly nearby in their own waste with no medical help.

More than 90 people have died in Bihar in the past two weeks while in Uttar Pradesh, 125 have lost their lives. A government spokesman in that state said 2,400 villages had been cut off.

Some good news however emerged in northeastern Assam state, where people began to return to their homes in all but one district as rains eased off.

In Bangladesh, at least 39 more fatalities were reported overnight, mostly children who drowned in the swirling waters, raising the overall toll to 120, government spokesman Shachindranath Halder said.

Some eight million people have been displaced in the severe flooding. Nearly 100,000 mud-built or tin-roofed houses have been completely destroyed, with the residents forced to live at government shelters, Halder said.

Water levels in the Brahmaputra and the Meghna rivers had significantly dropped by Sunday in the worst affected northern districts, the country's flood centre said, but the Padma - called the Ganges in India - was still rising.

In Nepal, where some 270,000 people have been affected by the floods, mostly in the southern plains bordering India, residents slowly began returning home as monsoon rains began to ease.

Home Minister Krishna Prasad Sitaula flew to the area on Sunday to inspect relief camps. - AFP/de