"In Kerala, I took stock of the situation arising in the wake of the devastating floods across the state. Joined a review meeting and undertook an aerial survey to assess the damage caused by flooding. The nation stands firmly with Kerala in this hour," PM Modi, who was accompanied by Mr Vijayan, tweeted.

Earlier in the day, the prime minister held a meeting with the Kerala chief minister and announced an immediate flood relief of Rs 500 crore for the state. This was in addition to the Rs 100 crore announced by Home Minister Rajnath Singh on August 12. Kerala, however, has sought an immediate assistance of Rs 1,000 crore. States have pitched in for aid as well.

"Kerala is facing its worst flood in 100 years," Chief Minister Pinarayi Vijayan, who has actively been monitoring the situation and rescue efforts in the state, said last evening. Till now, 42 navy, 16 army, 28 coast guard and 39 National Disaster Relief Force teams have been engaged in rescue operations. Another 14 NDRF teams are expected to join them shortly. The military has pushed in more than 300 boats. 30 military helicopters are being used in operation, and another four aircraft and three coast guard ships have also been brought in.

With no end in sight to the deluge, people all over the state of 33 million have made panic-stricken appeals on social media for help, saying they cannot make contact with rescue services. The naval airstrip in Kochi will be used for commercial flights from Monday as civilian airport remained flooded, officials said.

Thousands of people are still perched on trees and rooftops, waiting to be rescued. Water has even started entering relief camps. Other messages have been sent from people trapped inside temples and hospitals as well as their homes.

Hundreds of fishermen from coastal villages have joined the rescue efforts at Pathanamthitta, where helicopters are airlifting people to safer places. According to the weather department, since the beginning of June more than 321 centimetres of rain has fallen on the hilly central Kerala district of Idukki, which is now virtually cut off from the rest of the state. Just this season, rain in Kerala has seen a nearly-160 per cent rise above normal.

The government says 10,000 kilometres of Kerala's roads have been destroyed or damaged, along with thousands of homes. The damage is unparalleled. Industry has suffered too. On top of tourist cancellations, Kerala's valuable rubber industry has been hit severely by the floods. Electricity supplies to more than half the state have been cut.

The airport in Kochi has been shut at least till August 26 and flight operations have been shifted to state capital Thiruvananthapuram. Domestic airlines have been asked to keep a check on air fares for flights operating to and from Kerala. Telecom operators have announced free call and data services and other relief measures for a week for users in Kerala. Rail services across the state and the metro service in Kochi have been hit too. Transportation has collapsed, and both residents and tourists are stranded. Desperate non-resident Keralites from Australia, the US and the UK have been pleading with authorities, seeking help for their families.

Congress president Rahul Gandhi urged PM Modi to urgently declare Kerala a natural disaster. "The lives, livelihood and future of millions of our people is at stake," he tweeted.