The new record in Phalodi, a city in the desert state of Rajasthan, is the equivalent of 123.8 Fahrenheit and comes as a heatwave sweeps the nation.
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It tops a previous record of 50.6 Celsius set in 1956.
"Yesterday (Thursday) was the hottest temperature ever recorded in the country... 51 degrees in Phalodi," said BP Yadav, a director of the India Meteorological Department, told AFP on Friday.
Temperatures in northern India regularly hit the high 40s in May and June -- the hottest months of the year -- but topping 50 degrees is unusual.
The weather office has issued warnings of "severe heat wave" conditions across large parts of India's northern and western regions through the weekend.
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India declares a heatwave when the maximum temperature hits 45 degrees Celsius, or five degrees higher than the average for the area in previous years.
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