DHARAMSALA, India (REUTERS) - Early monsoon rains have swollen the Ganges, India's longest river, swept away houses, killed at least 60 people and left tens of thousands stranded, officials said on Tuesday.

The rains are at least twice as heavy as usual in north-west and central India as the June-September monsoon spreads north, covering the whole country a month faster than normal.

The National Disaster Management Authority said a response force of 12 teams of 45 people each had been in action since Sunday, in addition to the army and border police.

In the Himalayan state of Uttarakhand, where officials say at least 60 people had been killed, air force helicopters airdropped commandos to help rescue some of the tens of thousands of people unable to move because of the floods.

"We are on a war footing, we are working day and night,"said R. Rajesh Kumar, a district official in Uttarkashi, where two national highways have been blocked.

The district has set up 32 camps to provide food and water for about 5,000 pilgrims and tourists caught by the floods while visiting local holy sites. The Ganges is sacred to Hindus.

Rains, which were 48 per cent above normal across India up until June 16, are expected to ease up in the next week, according to weather department officials.

In the eastern state of Orissa, flash floods destroyed at least 678 houses and damaged crops in storage, the state's deputy relief commissioner, P.R. Mohapatra, said.

So far, the rains have not hit the summer sowing season in India, as planting of rice, sugar, cotton and other agricultural produce is not yet in full swing.

India is one of the world's biggest producers and consumers of grains and about 55 per cent of its farmland relies on the monsoon for water.

Heavy rain early in the June-September season makes planting easier, but if flooding persists, stagnant water can delay sowing or damage early rice shoots.