Authorities warned of more torrential rain and strong winds over the weekend, as hundreds of troops and local fishermen staged desperate rescue attempts in helicopters and boats across the southern state.
Kerala, popular among international tourists for its tropical hills and beaches, has been battered by record monsoon rainfall this year.
The state is "facing the worst floods in 100 years", chief minister Pinarayi Vijayan said on Twitter, adding that at least 324 lives have been lost so far.
India's Prime Minister Narendra Modi arrived in the stricken state on Friday night, Vijayan's office tweeted, with media reports saying the premier would undertake an aerial survey of the worst-affected areas on Saturday.
People all over the state of 33 million have made panicked appeals on social media for help, saying they cannot make contact with rescue services as power and communication lines are down.
"My family and neighbouring families are in trouble," wrote Ajo Varghese, a resident of the coastal city of Alappuzha, in a Facebook post that quickly went viral.
"No water and food. Not able to communicate from afternoon. Mobile phones are not reachable... Please help," he added.
Other distressed messages were shared online from people trapped inside temples and hospitals as well as their homes.
More than 30 military helicopters and 320 boats are attempting rescues across Kerala after some areas were engulfed by overflowing rivers, with residents seen swimming and wading through chest-high waters past partially submerged houses.
Authorities said thousands of people have been taken to safety so far but 6,000 more are still waiting for rescue.
"We are deploying more boats and the army to ramp up rescue operations," senior state government official P.H. Kurian told AFP.
Helicopters have also been dropping emergency food and water supplies, while special trains carrying drinking water have been sent to Kerala.
According to India's weather bureau, since the beginning of June more than 321 centimetres (126 inches) of rain has fallen on the hilly central district of Idukki, which is now virtually cut off from the rest of the state.
The Kerala government has said it faces an "extremely grave" crisis and Vijayan warned of further torrential rainfall hitting the region over the weekend.
The gates of dozens of dams and reservoirs across the state have been opened as water levels reach danger levels, inundating many other villages.
At least 310,000 people have been displaced and are taking shelter in more than 2,000 relief camps.
North and central Kerala have been worst-hit by the floods with the international airport in the main city of Kochi shut until at least August 26.
The home ministry announced separately that 868 people have been reported dead in seven Indian states including Kerala since the start of the monsoon in June.
Published : Jun 30, 2022
Published : August 18, 2018
By : Agence France-Presse Kochi, India