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 kilos (11 pounds) 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.