Relief teams are racing against time to rescue tens of thousands of stranded people in rain-ravaged northern India, as the death toll from flash floods and landslides nears 600.

Rescuers have recovered scores of bodies from the swollen Ganges river after torrential monsoon rains struck the Himalayan state of Uttarakhand, officials said.

Raging rivers have swept away houses, buildings and entire villages, and destroyed bridges and narrow roads leading to pilgrimage towns in the mountainous state, which is known as the "Land of the Gods" for its revered Hindu shrines.

Nearly 63,000 people, mainly pilgrims and tourists, are still stranded or missing

Uttarakhand home secretary Om Prakash says "575 bodies have been recovered so far", but warns the death toll is likely to rise.

"As per our records, 62,790 people are still stranded," he said.

He says a seven-member team of doctors and officials is heading to the popular Hindu pilgrimage site of Kedarnath "to collect the bodies lying there".

Dozens of helicopters and thousands of soldiers have been deployed to rescue the trapped people, almost one week after the rains hit.

Television images show paratroopers rappelling from military choppers to assist in rescue operations.

"We are running against time," Ajay Chaddha, chief of the army unit overseeing rescue operations in the state, was quoted as saying by the Times of India Saturday.

The Indian Express says rescuers have a "narrow window of just 48 hours" to complete their operations, with bad weather expected from Sunday night.

Meanwhile, a group of 20 trekkers including six Americans were rescued after they were trapped near a remote glacier since the rains struck last week.

"They were on a trekking trip but got trapped because of the landslides and flash floods," Neeraj Khairwal, a top official of Pittorgarh district, said.

"The chopper has landed there now and they are all safe."

Such a disaster has 'never happened in Himalayan history'

The army has managed to make contact with nearly 1,000 people stuck in mountains near Kedarnath, the NDTV news network reported.

State chief minister Vijay Bahuguna on Friday said it would likely take another 15 days to rescue all of the trapped tourists.

He attacked the India Meteorological Department (IMD) for not issuing adequate warning ahead of the heavy rains, which struck earlier than expected, saying the local government was unable to prepare for the deluge and evacuate people on time.

"This kind of disaster has never happened in Himalayan history," he said.

"The IMD warning was not clear enough."

Distraught relatives clutching photographs of missing family members have been waiting for days outside Dehradun airport hoping for news of their loved ones.

Indo-Tibetan Border Police help flood evacuees across a raging river in Ghangaria ( AFP: ITBP )

Amit Thakur, 40, says his 11-year-old nephew has been missing since their family-run hotel collapsed last week.

"I just hope the army will trace our little boy," Mr Thakur said.

"I have been standing outside the airport for the last three days to get any information about him."

The military operation, involving some 50 helicopters and more than 10,000 soldiers, is focused on reaching those stranded in the holy town of Badrinath after earlier finding widespread devastation in the Kedarnath temple area.

"Our soldiers have rescued more than 50,000 people, including around 16,000 people who were evacuated today," Home ministry spokesman Kuldeep Singh Dhatwalia said.

Another 17 people have been killed in the adjacent state of Himachal Pradesh, a senior government official said.

Floods and landslides from monsoon rains have also struck neighbouring Nepal, leaving at least 39 people dead.

Pictures show pilgrims, aided by soldiers, using ropes and makeshift ladders to climb down cliffs and cross rivers.

Rescue workers who managed to reach those stranded were racing to cut down trees and clear vegetation to allow military helicopters to land and evacuate those most in need, a state official said.

"Thousands of tourists are waiting in the dense forests. They had all taken refuge in the jungle after hotels and other buildings collapsed," the state's principal secretary Rakesh Sharma said.

"We are trying all possible ways to rescue them. Roads are totally destroyed."

AFP