The mercury shattered all records in Delhi with parts of the national capital recording an all-time high of 48 degrees Celsius on Monday.
The city's previous high of 47.8 degrees Celsius was recorded in Palam on June 9, 2014.
"The Palam Observatory recorded an all-time high of 48 degrees Celsius Monday. The factors that led to this are dry westerly winds, no effect of a western disturbance in the plains and intense heating in the month of June," said India Meteorological Department regional weather forecasting chief Kuldeep Srivastava.
"Southwesterly winds on Tuesday may cause the temperature to drop by one or two notches. However, the heat wave will persist," he said.
The Safdarjung Observatory, which provides official figures for the city, recorded a high of 45.6 and a low of 27.2 degrees Celsius.
Hot dry winds- loo - swept the city, compounding the woes of people who had to venture out for work.
In large areas, a heatwave is declared when the mercury touches the 45-degree mark for two consecutive days and a severe heatwave is when the temperature soars to 47 degrees Celsius for two days on the trot, according to the India Meteorological Department.
In small areas, like the national capital, a heatwave is declared if the maximum temperature is recorded at 45 degrees Celsius even for a day, it said.
According to private forecaster Skymet, Monday's highest temperature was recorded in Rajasthan's Sri Ganganagar at 48 degrees Celsius.
Temperatures in parts of Bihar and central and western regions recorded a surge to 47 degrees Celsius. In northern India, mercury hovered around 45- 46 degrees Celsius.
There could be relief for people in Delhi and the surrounding areas with pre-monsoon showers predicted on Tuesday.
"A cyclonic circulation over Rajasthan will cause rains in Delhi and surrounding areas on Tuesday evening. It will lead to a drop in the temperature," said Mahesh Palawat, Director at Skymet.
"Rains will occur on Wednesday and Thursday as well. Later, there will be no heatwave,” he added.