A city in northern India has shattered the national heat record, registering a searing 51 degrees Celsius -- the highest since records began -- the weather office said Friday.

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.

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 B.P. 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.

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.