The death toll from the heaviest rain to fall on Kashmir in 50 years rose to more than 400, with thousands still trapped on rooftops.
Residents have criticised Indian and Pakistani authorities for not doing enough to help them.
On the Indian side of the heavily militarised Line of Control that divides the Himalayan region, the city of Srinagar lay submerged along with more than 2,000 villages.
"The damage is shocking," a senior official from India's National Disaster Response Force said in New Delhi.
"People have been stranded on the rooftops of their homes for the last three days in some parts of Kashmir."
The official, who requested anonymity, said he would have deployed disaster-response teams earlier, but "we were all caught off guard because there was not a single warning issued by the weather office. The flash floods took us by surprise".
India's meteorological department had forecast heavy rain in Kashmir last week, but the Central Water Commission, which issues flood advisories, has been criticised by Indian media for not warning the state.
Around 47,000 people have been evacuated from their homes in India, where 217 were reported dead.
The Indian Air Force has air-dropped more than 550 tonnes of relief material, and 80 medical teams have established emergency health services in government schools and state-run health care centres.
In Pakistan, the death toll was comparable, with at least 231 people reported dead across the country, including Pakistan's side of Kashmir.
Indian Soldiers rescued families using boats or airlifted them from rooftops by helicopter after the river Jhelum burst its banks in Srinagar, but many more remained stranded.
"Fortunately, it is not raining in Kashmir today and we are now getting a chance to send our teams across the region to help tens of thousands of people who have been displaced," Indian Defence Ministry spokesman Sitanshu Kar said.
An official at Pakistan's State Disaster Management Authority, said the volume of rainfall had rendered contingency plans useless.
He said the district of Haveli, which straddles the de facto border between Indian- and Pakistani-controlled Kashmir, had got 400mm of rain in a day, which had "no parallel in the past 50 years".
The International Federation of Red Cross and Red Crescent Societies said this year's monsoon rains had killed more than 1,000 people in India alone.
The flooding is the first major humanitarian emergency under India's new prime minister, Narendra Modi, but also comes at a difficult time for Pakistani Prime Minister Nawaz Sharif, who has faced weeks of street protests aimed at forcing him out.
