The floods were triggered by torrential monsoon rains across Orissa state, causing water levels to rise and overflow river banks, sparking an operation that saw helicopters drop off emergency food packets to help the stranded.

"We are face-to-face with yet another bitter flood that has claimed 18 lives with another six people reported missing," Orissa's disaster management minister Surya Narayan Patra told AFP.

He said the state government had evacuated tens of thousands of people from their waterlogged homes and was enacting relief measures to help a total of 1.7 million people affected by the floods.

Orissa's special relief commissioner Pradeep Kumar Mohapatra told reporters that access to 877 villages was completely cut off due to rising water levels and that 11,000 houses had been damaged.

"The numbers of people affected have doubled in just a few weeks and there is more rain to come," said John Roche, India's country representative for the Red Cross.

"Thousands have lost homes and livelihoods, leaving many wage-earners with no choice but to migrate to nearby towns to find work."

The strength of the annual June-September downpour is vital to hundreds of millions of Indian farmers and to economic growth in Asia's third-largest economy which gets 80 percent of its annual rainfall during the monsoon season.

Floods in neighbouring Pakistan have killed 138 people in the last month and affected up to five million more.