Homes, farmland and roads flooded following weeklong rain that affected India and Sri Lanka.
Rescue operations continued in inundated southern India on Friday after the worst flooding in decades stranded tens of thousands of people.
At least 269 people have been killed because of flooding in Tamil Nadu state in recent days with more than 1,000 critically injured.
Speaking in parliament, Rajnath Singh, the interior minister, described the situation as an “unprecedented calamity”.
Authorties were trying to reach people as water levels in the main rivers – Adyar and Kumbh – began receding in the city of Chennai. The government has set up 97 relief camps that are currently providing food and shelter to an estimated 62,000 people, Associated Press reported.
India’s Prime Minister Narendra Modi, who did an aerial survey of the devastation, announced $150m (10bn rupees) in federal aid to carry out relief operations in the flood-affected areas of the city and its adjoining areas.
“I have seen the damage and misery caused by the extremely heavy rainfall. The government of India stands by the people of Tamil Nadu in their hour of need,” Modi said in a statement.
Chennai, India’s fourth-largest city, and surrounding areas have received two blasts of heavy rain so far in the October-December wet season. The country’s Meteorological Department predicted more rain until Sunday.
Singh said at least 2,000 disaster relief and military personnel were deployed.
Forty percent of the area’s telephone lines have been knocked down by the floods and power connections had to be disconnected for safety reasons, the minister said.
Hundreds of people are still stranded, food is running short, and ATM machines are down, NDTV news channel reported.
The floods have cut off more than three million people from basic services and hampered rescue efforts by the army, which has so far evacuated 18,000 people from rooftops and outlying villages, Reuters reported.
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Civilians volunteered to help those stranded or in need of urgent medical help. People used social media platforms such as Facebook and Twitter to pass on important information.
City authorities deployed bulldozers and bags of concrete to repair collapsed roads, while several bridges were under water as urban lakes in the low-lying coastal city overflowed.
Train services and flights to Chennai remain cancelled. The navy pressed fishing boats into service to rescue people from the worst-hit suburbs and take them to temples, schools, and wedding halls.
Urban planners said haphazard construction work, faulty drainage systems, and a build-up of rubbish had contributed to the flooding.
More than 5,000 houses were under water with many people still trapped on rooftops, while others crowded into relief camps.