Chennai is currently being lashed by the worst rains it has seen in a hundred years. The airport and railway stations are shut; supplies of essential goods have dried up: and the death toll, at last count, was 188.
If you are in the city you can now use Facebook's Safety Check tool to let family and friends know you are safe -- helpful, because mobile networks and landlines are particularly unreliable right now.
The tool, which lets Facebook users mark themselves and others as safe after tragedies -- both natural and human -- was last activated by Facebook in the wake of the Paris attacks in November when terrorists from IS gunned down over 130 people in the city.
People outside the affected area can search for friends who have marked themselves "safe" and also for those who have yet to check in to the tool.
Safety Check was originally launched in October 2014 and was first activated during the Nepal earthquake in April that killed nearly 9,000 people and injured over 21,000.
If you're in Chennai and want to mark yourself or someone else safe, click here to use Facebook's tool.
Google has launched their crisis response page titled South India Flooding with resources such as emergency helpline numbers, list of relief centres and crowdsourced maps. The page also has video feed from YouTube.
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