Although Chennai is frequently hit with heavy rains this time of the year, experts say unchecked development and bad urban planning leads to destruction and chaos. Climate change caused by global warming has also contributed to the problem, making extreme rainfall more likely and more frequent.
Parts of Chennai has been facing power cuts as the power department shut off the supply to avoid incidents of electrocution.
Footage showed people being rescued on rubber boats as muddy brown waters gushed into their homes. The National Disaster Response Force and the army are helping in the rescue work.
Others were seen wading through knee-deep water to get essential commodities. Most of the main streets have been waterlogged since Saturday, bringing the city to a standstill.
Several people on social media said the situation was as grim as the floods of 2015 when over 200 people had lost their lives in the state.
All schools and colleges in Chennai and neighbouring districts have been shut and officials have advised against travelling in hazardous conditions. Fishermen along the coast have also been asked not to venture into the sea.
Chennai's municipality said it had opened up relief centres and medical camps across the city and was distributing food to flood victims.
Tamil Nadu's Chief Minister MK Stalin said he had asked all his ministers to help in recovery efforts.