Soldiers were battling Sunday to rescue thousands of people trapped in Indian Kashmir's worst flooding for half a century which has left more than 100 people dead and the main city of Srinagar under water.

Some 350 villages have also been submerged since torrential monsoon rains triggered flooding across the picturesque Himalayan region of Jammu and Kashmir.

Across the border in Pakistan, landslides, flash flooding and house collapses also from days of heavy rain have left another 128 people dead, officials there said.

The Jhelum river, swollen by heavy rain, flooded large parts of Srinagar on Sunday and forced frantic residents onto rooftops, with reports the first floors of a children's hospital and of another hospital were underwater.

"I want to appeal to people not to panic," Jammu and Kashmir state chief minister Omar Abdullah told reporters.

"I know the situation is bad but they should stay above the water level... it may take up to an hour but we will reach them and take them out," he said.

"We are taking all the measures to ensure that we can reach the maximum number of people," he said, adding that 110 people have died in the state so far.

Hundreds of troops, police and other emergency personnel, backed by helicopters and boats, have been deployed across the state to reach those stranded, with 11,000 people rescued so far, officials said.

Prime Minister Narendra Modi flew to the normally picturesque, remote region to meet Abdullah and emergency response officials amid concerns the death toll could jump.

A police official in Srinagar, a city of 900,000, said he feared the true extent of the devastation was not yet known because phone networks were down and areas cut off.

"We are in a catastrophic situation," he told AFP on condition of anonymity, adding that Srinagar's police headquarters was under water.

"Many people may have died and houses collapsed but we are not getting to know much (information)," he said.

- Trapped in homes -

An AFP reporter in Srinagar was forced to the third floor of his house after water flooded the second, with no sign of emergency officials to evacuate him.

"We will have to move to the roof but we are also worried about the building collapsing," he said adding that water has risen about 12 feet (3.6 metres).

From his window in the centre of the Muslim-majority's city, he said he could see other residents on their roofs and top storeys of their homes, their arms in the air praying.

Another resident, Aakifa Javaid, said her local mosque announced on loudspeakers that "it would be a difficult night, no one should sleep" as the river overflowed its banks.

Like hundreds of others in her neighbourhood in the city's north, she fled in the middle of the night when the water reached her home.

An army headquarters was also under water along with some government buildings, while roads and bridges throughout the region have been cut or washed away.

Hundreds of soldiers, backed by 22 helicopters and four aircraft, have fanned out across the Kashmir Valley and the rest of the state to rescue those stranded, deliver aid and restore phone lines, said national cabinet secretary Ajit Seth.

"About 70 boats have (also) been airlifted, 20 have already left from Palam (in Delhi) a short while ago," he told the NDTV network.

Several thousand villages across the region, which has long been in the grip of a deadly separatist insurgency, have been hit and 350 of them are submerged, the home ministry said late Saturday.

The ministry put the death toll at 116 across the state, although the chief minister said the figure was 110, with another 128 across the border in Pakistan which has also been hit hard by the floods.

Heavy rains were, however, easing and have stopped altogether in parts of Pakistan following the floods that have damaged 108 villages as well as farmland in that country, the National Disaster Management Authority spokesman said.

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