Indian army helicopters rescued stranded families from rooftops and dam gates were thrown open as incessant torrential rain brought fresh havoc on Thursday to the state of Kerala where about 100 people are feared dead.
Hundreds of extra troops were deployed in the southern state, a popular tourist destnation, as the government issued a "red alert" over the region's worst floods in decades.
Chief Minister Pinarayi Vijayan discussed the situation with Prime Minister Narendra Modi, who said he had ordered the defence ministry to intensify rescue and relief operations across Kerala.
State authorities said the death toll was 72 but officials and media reports said up to 30 more people were feared killed on Thursday in landslides and as rivers burst their banks, flooding scores of villages.
At least eight people were reported dead and 15 others, including a three-month-old infant, were trapped inside three houses hit by a landslide near an irrigation dam in Malappuram district, the Hindu newspaper said.
Authorities said many people were trapped inside their houses. More than 60,000 people have sought refuge in relief camps.
"At least 6,500 people are stranded in different parts of Kerala and the situation in three districts is particularly grim," a state disaster management official said.
Kerala, famed for its pristine beaches and verdant landscape, is battered by the monsoon every year but this year's damage has been particularly severe. Floods have also caused havoc in other states, including Karnataka and Madhya Pradesh.
About 540 members of the army, navy and air force were sent to Kerala on Thursday to join the rescue effort.
The army said it had rescued scores of people with helicopters. Defence forces and government boats were also used in an increasingly desperate rescue operation.
Authorities appealed for victims to stand in open fields or on rooftops away from trees so helicopters were not damaged during rescue efforts.
Army helicopters also dropped food packets and drinking water to some of the worst-affected districts.
The government says 10,000 kilometres of Kerala's roads have been destroyed or damaged and hundreds of homes lost.
It has ordered the opening of gates at 34 dams and reservoirs where water levels had reached danger levels.
Indian television channels showed cars and livestock being washed away in the floods and men and women wading through chest-high waters that had gushed into their homes.
Many residents used social media to send distress calls, some with video.
Greeta Mathew pleaded for help for her family in a Twitter message.
"Anybody reading this,PLZ HELP. My relatives are stuck on the upper floor of house with an 8 months pregnant lady, in Edayaranmula, Pathanamthitta dist. All rescue control rooms' numbers busy. No rescue team reached yet. No contact with family since last evening," she said.
North and central Kerala has been worst hit by the floods but all 14 of the state's districts have been put on alert as heavy rain is predicted for several days.
In the main city of Kochi, the international airport was closed until at least Saturday because of flooding. Departures were cancelled while incoming flights have been diverted to other airports in India.
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India's civil aviation minister Suresh Prabhu said all domestic and foreign airlines had been asked to reschedule their Kochi flights from either Thiruvananthapuram or Kozhikode.
"For international flights, this will require special dispensation which has been granted considering the emergency DGCA (Directorate General of Civil Aviation) is coordinating," Mr Prabhu said on Twitter.
All public transport has been stopped with many buses abandoned in the road.
The floods have also disrupted celebrations of Onam, one of the main festivals in the state of about 33 million people, which began on Wednesday.
Elsewhere, eight people were swept away on Wednesday after a sudden water surge hit a popular picnic in Madhya Pradesh state. Another 45 stranded were rescued on Thursday by police.
The US embassy last week advised Americans to avoid Kerala, which was visited by more than one million foreign tourists last year, according to official data.