New Delhi  - India on Friday carried out one of the biggest evacuation operations in its history, rescuing nearly 1 million people marooned in the flood-hit eastern state of Bihar, officials said.

The floods came when heavy monsoon rains caused the Kosi River to breach its banks as it entered the state from Nepal in the north and change its course. At least 57 people have died in the floods.

More than 3.5 million people have been displaced by the floods, nearly 2 million of them in the five worst-affected districts of Madhepura, Saharsa, Supaul, Araria and Katihar.

The Bihar government, with help from the army and voluntary organizations, has been carrying out evacuation operations and removed more than 153,000 people to safer areas so far, state officials said.

"But heavy rains disrupted the rescue and relief operations since Thursday, adding to the woes of thousands who are struggling to survive and spending nights on roofs, railway tracks and canal embankments," said Anil Kumar, an official in the state's disaster management department.

Bad weather also affected air drops of relief material, including food packets, over the past two days.

Indian Prime Minister Manmohan Singh, who visited the affected areas on Thursday, called the floods a "national calamity" and announced an aid package of 234 million dollars.

Local media reported there was a shortage of boats for rescue operations and many of the victims were angry that they were moved to temporary shelters without basic amenities.

"The government has just given us a sheet of plastic to protect ourselves from the rain," a flood-victim told the NDTV news channel. "Local people gave us some food. You can see how we are living in this filth."

There were no doctors or supplies of medicines in areas at risk of disease.

Many of those marooned have been without food and water for several days. Only 2,500 food packets could be distributed on Thursday while thousands went hungry.

"People are going to die, and nobody is going to rescue them," an angry villager told the news channel.

Road links, water and electricity supplies have been cut off, and rail operations have been suspended because tracks are submerged under water.

A UNICEF report said there were fears of outbreaks of infectious diseases as thousands crowded relief camps.

In Bihar's neighbouring state of Uttar Pradesh nearly 725 people had been killed in monsoon-driven floods this year, the federal Home Ministry said.

More than 1,650 people have died in this year's monsoon rains across India - in the states of Assam, Arunachal Pradesh, West Bengal, Orissa, Jharkhand and Uttar Pradesh.

India's monsoon season lasts from June to October but came a few weeks early this year. (dpa)