Nearly 50,000 people were evacuated to higher ground as rains intensified in the south-eastern state of Tamil Nadu, while a key airport in neighbouring Andhra Pradesh state was shut down because of flooding.
"Some of the low-lying areas have been marooned. Transportation has also been disrupted in several places. People are being shifted to higher places," a top official in the Tamil Nadu relief commissioner's office said.
Officials said 56 people have died in the rains in Tamil Nadu, while another 26 have lost their lives in the south-western state of Karnataka.
The Karnataka state government has called on the army for help as the driving rain has caused breaches in the state's Cauvery River, leading to floods in some areas.
Weather officials said the rains had been caused by a low pressure system over the Bay of Bengal which was likely to stay put over the next two days.
Gale winds were also expected to lash the region. State authorities have warned fishermen not to venture out to sea.
Tamil Nadu Chief Minister Jayaram Jailalitha met with top officials Thursday to review the situation and work out rescue and relief efforts for the rain-affected areas.
Flights at Vishakhapatnam airport in Andhra Pradesh state had been suspended for the last two weeks because of the rains.
Officials from the Airports Authority of India said Chennai's international airport had also been shut down on Thursday, and four flights, including three international ones, were diverted to Bangalore.
"The annual monsoon rains have arrived earlier than usual over southern India. Now this wet weather will last for at least another two months. It is a huge challenge for the administration," a Tamil Nadu official said.
Unlike the rest of India which experiences monsoon rains between June to September, southern India gets monsoon rains in November and December.