At least 280 people have been killed in Pakistan and more than 500 others injured, the government there said, CNN reported.
And at least 200 people have died in flooding in Indian-administered Kashmir, Indian Home Ministry spokesman Kuldeep Dhatwalia told CNN.
Some volunteers in that country fear the toll could be much higher.
"Our teams on the ground in Srinagar have seen a number of bodies floating. The casualty is believed to be much more than what his being officially reported," said Syed Zafar Mahmood, president of the nonprofit Zakat Foundation of India group. "A number of villages have been washed away."
By Saturday, military and other emergency crews were able to rescue more than 276,000 people from parts of the flood-ravaged region under Indian control, according to officials.
Home to 12 million people, the state of Jammu and Kashmir is India's 19th most populous province.