Floodwaters receded in Kerala on Monday, leaving Indian rescuers the grim task of retrieving bodies as the death toll from the worst monsoon rains in a century rose above 400.

With nearly three quarters of a million people packed into relief camps in the southern state, known for its tourist beaches and hill resorts, authorities also fear outbreaks of disease. After more than a week of fierce downpours, rainfall eased on Monday and flood levels fell in some districts. Army helicopters and boats kept up missions to find trapped survivors and drop food and water in isolated villages.

The Indian government has declared the floods a "calamity of severe nature", a home ministry official told AFP. Officials said 22,000 people were rescued on Sunday. At least 30 bodies were also found, taking the death toll above 200 since the torrential rain started falling on August 8 and more than 400 since the monsoon started in June.

At least 1,000 were feared stranded in five villages around Chengannur, one of the districts worst hit by the deluge. An Indian Navy team made a temporary rope bridge across a stream in Thrissur district on Sunday to rescue 100 people stranded for days.

Commercial flight operations to Kochi, the state’s main city, resumed Monday after the navy opened its airstrips for small passenger aircraft. The city’s international airport has been ordered shut until Sunday.

The floods have left widespread desolation in the city. Mumthaz fled her home in the Malikapeedika district of Kochi with her daughters aged 13 and nine last Thursday. She went to her husband’s parents in another neighbourhood but within a few hours even that was also flooded and they had to be rescued and taken to a relief camp.

"It was surreal. The water was close to the knees at one point and within a few minutes it was touching five feet with a current so strong that we saw big cars floating like tin cans," said Mumthaz, who has only one name.

Kerala Chief Minister Pinarayi Vijayan said the priority now was to provide clean drinking water and restore power supplies to the state of 33 million people. "The total number of people taking refuge at the 5,645 relief camps has risen to 724,649," Vijayan told reporters on Sunday.

He said health officers would be deployed in each village to check the spread of communicable diseases. Thousands of army, navy and air force personnel have fanned out to help those stranded in remote and hilly areas.

Dozens of helicopters have been dropping tonnes of food, medicine and water over areas cut off due to damaged roads and bridges. In the worst-hit areas such as Thrissur and Chengannur, rescuers searched inundated houses, discovering the bodies of those trapped by the fast rising floodwaters.

"They didn’t think that it would rise this high -- 10 to 15 feet at some places -- when the initial warnings were issued," said Ashraf Ali K.M., who is leading the search in the small town of Mala in Thrissur.

Fishermen have sailed inland from Kerala’s coast to join the search, as volunteers set up soup kitchens and an international appeal was made for financial help. The state government said each fishing boat would get 3,000 rupees for each day of work and that authorities would pay for any damage to them. The floods have caused an estimated $3 billion in damage but the bill is likely to rise as the scale of devastation becomes clearer.