All 20 people on board a military helicopter were killed when it crashed in flood devastated northern Indian, the country's air force chief said on Wednesday.

The helicopter carrying soldiers, police and rescue workers crashed on Tuesday afternoon during a rescue mission in the Himalayan state of Uttarakhand where flash floods and landslides have killed some 1,000 people.

The death toll from the crash rose from eight to 20 after rescue workers continued their search for bodies at the crash site in a mountainous area of the state, air force officials said.

"Twenty warriors have died. It is a loss for the entire nation," Air Chief Marshal NAK Browne said in the state capital Dehradun.

"It is difficult to say at the moment how the plane crashed, if it was because of a technical fault or poor weather conditions," he said. "The cockpit recorder has been found," he added.

The helicopter had been flying a mission near the holy pilgrimage area of Kedarnath, the epicentre of the disaster.

Those killed were from the National Disaster Response Force, the Indo-Tibetan Border Police and the air force, officials said.

The military, including 60 helicopters, has been leading efforts to evacuate some 6,000 pilgrims and tourists still stranded throughout the state since the floods hit on June 15.

Raging rivers have swept away houses, buildings and even entire villages in the state, which was packed with travellers in what is a peak tourist season.

More than 1,000 bridges have been damaged along with roads, cutting off villages and towns.

Multiple agencies undertaking relief and rescue operations are becoming increasingly concerned about the spread of disease, particularly from the bodies of those who perished in Kedarnath.

Mass cremations of hundreds of bodies were delayed on Tuesday, as heavy rains hampered preparations.

"We want to cremate the bodies but the rains are not allowing the process to start," said senior disaster management official K.N Pandey.

Eight dead as India floods helicopter crashes: military
Rudraprayag, India (AFP) June 25, 2013 - A helicopter helping victims of devastating floods in northern India crashed near a pilgrimage site Tuesday, killing all eight people on board, as fresh rains hampered the bid to rescue thousands still stranded.

Around 60 air force helicopters are taking part in the rescue operation in the Himalayan state of Uttarakhand where more than 1,000 people have been killed by floods and landslides since the beginning of last week.

The helicopter which crashed on Tuesday afternoon was on a medical mission near the pilgrimage site of Gaurikund, air force officials told AFP .

"The eight persons on board including five crew members sustained fatal injuries," said a statement sent to AFP.

Gerard Galway, a spokesman for the air force in Uttarakhand, said the reasons for the crash were being investigated.

The military has been leading efforts to evacuate some 6,000 pilgrims and tourists still stranded throughout the state since the floods hit on June 15.

Raging rivers have since swept away houses, buildings and even entire villages in the state, which was packed with travellers in what is a peak tourist season.

More than 1,000 bridges have been damaged along with roads, cutting off villages and towns.

The scale of the rescue effort has been prompted in part by fears that failure to act swiftly could trigger widespread disease from hundreds of bodies which have yet to be recovered.

As well as trying to rescue stranded victims from remote parts of the mountainous state, relief workers have been busy spraying disinfectant and are preparing for a mass cremation in the holy town of Kedarnath which is one of the worst-hit areas.

But although tonnes of wood have been flown by helicopter into the area for the cremation, the ceremony had to be postponed on Tuesday following more heavy downpours.

Some 6,000 pilgrims and tourists are believed to be still stranded throughout Uttarakhand, known as the "Land of the Gods" for its revered Hindu shrines.

They were caught unawares on June 15 when flash floods, triggered by earlier than expected monsoon rains, swept through the area.

"We are spraying disinfectant in the flood-affected areas to prevent the spread of water-borne diseases," state medical officer K.D. Sharma said.

The move came as fresh rains and landslides hampered efforts by the military to evacuate people since the floods hit the state.

The United States has pledged funds for the rescue effort and UN chief Ban Ki-moon voiced his sadness at the scale of the disaster.

"The secretary-general is saddened by the loss of life, and the damage to homes and infrastructure in India as a result of the torrential floods in the northern state of Uttarakhand over the last week," said his office.

A police official in charge of organising the cremations said belongings and documents recovered from bodies will be used to help with identification while DNA samples will also be collected.

"Under no circumstances can we allow an outbreak of an epidemic," senior disaster management official K.N. Pandey told AFP.

"We have reports that many stranded people are suffering from diarrhoea and other ailments and have decided to cremate the corpses near the Kedarnath shrine," he said.

A senior official warned that the death toll of 1,000 could rise dramatically as the grim task of collecting the bodies from rivers and from under flattened villages and other debris continues.

"From the feedback we are getting from people on the ground, people working in scavenging bodies, our estimate is the toll could be anything between 4,000 and 5,000," a senior disaster management official who did not want to be named told AFP.

Helicopters and soldiers have evacuated tens of thousands of people from the floods, while tonnes of food and other emergency supplies have been dropped to those still stranded.

Unmanned drones have also been deployed to scan the thick jungles to find those still awaiting rescue, officials said.

Thousands of soldiers along with the Indo-Tibetan Border Police have been evacuating people by foot, using harnesses and erecting rope bridges across flooded rivers to help them to safety.