Police in the hard-hit Indian state of Bihar say a boat carrying flooding refugees capsized, drowning 20, and hundreds of thousands more are stranded without food or water, the BBC reported Saturday.

The disaster was caused when the River Kosi, which separates India from Nepal, changed its course after the dam breach, resulting in more than 250,000 homes destroyed and a total of 3 million people affected.

More rain is expected and rescuers are racing to reach those affected before the river rises again, the BBC said.

U.N. Secretary General Ban Ki-moon said Saturday he is extending "his deepest condolences to those affected, especially to the families of those who have been killed or who are missing," the Press Trust of India reported.

UNICEF has delivered tarpaulin sheets and other items to 8,000 families in India and more than 10,000 people in Nepal.

Nepal has apologized to India for the breach, CNN-IBN reported, quoting Foreign Minister Upendra Yadav as saying the breach was not noticed in time.