Millions of people are stranded by flooding in northeast India with concern growing about food and water supplies, and officials said on Wednesday that water levels of a major river were rising even further.

At least 5.8 million people have been displaced — a million more than on Monday — and some 30 have died in the past two weeks in the tea-growing state of Assam due to the monsoon rains, local government officials said.

"The water level of the Brahmaputra and its tributaries have started showing a rising trend since midday and flowing above the danger mark in at least 10 places," an Assam Disaster Management Authority official said.