Army and air force troops worked to rescue thousands of people stranded in Indian-controlled Kashmir and northern and eastern Pakistan, where flooding and landslides have caused more than 320 deaths.
Six days of rains in Indian Kashmir have left more than 120 people dead in the region's worst flooding in more than five decades, submerging hundreds of villages and triggering landslides, officials said.
In neighbouring Pakistan, more than 205 people have died and thousands of homes have collapsed.
In Islamabad, Pakistan's National Disaster Management Authority spokesman Ahmad Kamal said the death toll had risen to 205 people with at least 383 more injured over the past six days.
Pakistani troops were helping civilian authorities in rescue operations and in getting aid to stranded villagers, the Pakistani army said in a statement.
So far nearly 9,000 people have been evacuated from nearly 530 villages that were inundated by flood waters, Mr Kamal said.
He said authorities were preparing for worsening conditions as the waters of the Chenab and Indus rivers were rising.
Pakistani TV channels showed pictures of flooding from different cities and villages, with the water raging through streets, causing heavy losses.
Mr Kamal said flash floods and landslides had killed 131 people in Pakistan's Punjab district, and 74 others in the Kashmir and Gilgit areas.
The Kashmir region in the northern Himalayas is divided between India and Pakistan and claimed by both. Two of the three wars the countries have fought since independence from Britain in 1947 have been over control of Kashmir.
In India's portion of Kashmir, more than 5,200 people have been rescued, said OP Singh, director of India's National Disaster Response Force.
Blankets, medicine and food were being supplied to people stranded on rooftops, he said, as most parts of Srinagar, the main city in Indian Kashmir, were submerged.
At least 450 villages in Indian Kashmir have been submerged and 2,000 others have been affected by the floodwaters, officials said. All schools, colleges and offices have been shut, and electricity and drinking water supplies have been limited.
The floods and incessant rain hit the power supply in several districts in Kashmir after electric pylons collapsed or wires snapped. Mobile phone services by private operators were disrupted and landline telephone networks were also not working, leading to panic among many people stranded with no means of communication.
Omar Abdullah, chief minister of India's Jammu and Kashmir state, said the floods were the worst to hit Kashmir in decades.
"This is an unprecedented situation and we are doing the best we can under the circumstances. Please don't panic, we will reach you, I promise," he tweeted.
Prime minister Narendra Modi, who surveyed the flood-hit areas by helicopter on Sunday, called the flooding a "national disaster". He promised the state an additional 10 billion rupees (£103 million) for aid and compensation to those hit by the floods.
He also sent a letter to his counterpart Nawaz Sharif offering India's help in relief efforts to the Pakistan-controlled portion of Kashmir. There was no immediate response to the offer.