The worst monsoon flooding in a century has left hundreds dead and upwards of a million people displaced.

Indian health authorities have started preparing defences against the spread of disease in flood-hit Kerala state, as water receded and a huge clean-up gathered pace.

By Monday, the death toll in the southern state had reached 370 and the number of people displaced was upwards of a million.

Incessant rain since August 8 has caused the worst floods the region has experienced in a century and triggered landslides.

Dozens of people are missing and hundreds of thousands are sheltering in thousands of makeshift relief camps, state officials said.

“The biggest challenges immediately ahead are cleaning of the flood-hit houses, rehabilitation, and prevention of water-borne diseases,” said Mahesh P, a village-level officer from Rayamangalam, some 45km from Kerala’s financial capital of Kochi.

Al Jazeera’s Andrew Thomas, reporting from a relief camp in Kayamkulam, said the huge number of people gathered in the shelters increased the risk of disease spreading.

“When you have more than three quarters of a million people in temporary camps like this one, disease is always a risk,” he said.

“You have lots of people in a small space, and without the things they would normally have at home, like clean water and regular food.”

Survivors who spoke to Al Jazeera said even places of shelter were under threat.

One woman, a 45-year-old named Ayisha, said she was in a hospital when waters threatened those inside.

“We were on the ground floor…water rushed into the place where we slept, the speed of water was way too fast,” she said.

“The volunteers immediately transferred us to the first floor. Since the ground floor was filled with water, it was impossible for us to leave the building.

“We were saved by breaking the walls and a (make-shift) bridge.”

Disease control

Light to moderate rain was expected across Kerala on Monday, bringing some respite to rescue workers, who have been battling rising waters and mudslides to reach tens of thousands of stranded villagers.

Rainfall in the state during the June-September monsoon season has been more than 40 percent higher than normal, with torrential rain in the last 10 days forcing authorities to release water from dozens of dangerously full dams, sending surges into rivers that then overflowed their banks.

At least 40,000 animals have died as a result of the floods, according to the animal welfare NGO, People for Animals, which is helping the government in its response.

As flood waters receded from, thousands of animal carcasses floated away with them.

“We’ve found the decomposing bodies of dogs and cows floating on the water,” said Abdurrahman, a volunteer helping the relief effort.

Anil Vasudevan, who handles disaster management at Kerala’s health department, said the state was preparing to battle any outbreak of diseases in the relief camps and preventive medicines were being distributed.

Mahesh said villagers had all pulled together to rescue people and prevent an even bigger disaster.

“The bulk of the credit for the rescue goes to the ordinary citizens. The army, the navy, the local authorities assisted them,” Mahesh said.

“The flood has bonded the people like never before, with people sharing whatever they had.”

Kerala Chief Minister Pinarayi Vijayan said there was no shortage of food in the state as traders had stocked up ahead of Onam, the state’s biggest festival which falls on August 25.

The state has cancelled all official celebrations in connection with the Hindu harvest festival.

Additional reporting by Aslah Kayyalakkath.