This is the first time in nearly six decades that the mercury touched that record mark in the Indian capital.
Roads remained deserted and residents struggled to get any respite from the sweltering heat as air-conditioners and water-coolers failed to fight the heat.
Frequent power cuts were reported from several parts of the city and the adjacent satellite cities of Noida and Gurgaon.
“The heat is unbearable,” Manju Kumari, a domestic helper in Noida, told The National. "We do not have a water-cooler, but the ceiling fan also doesn’t work because of a power cut every now and then. We are sleeping on the terrace every night."
In the capital's Mungeshpur in the north-west part and Najafgarh areas, the mercury rose to 49.2°C and 49.1°C respectively on Sunday, breaking the previous record of 49°C in May, 1966.
The city's main Safdarjung observatory recorded 45.6°C.
The Indian capital has 11 weather stations, up from two a decade ago, to monitor ultra-localised weather patterns.
The weather office, though, said that the city recorded an average temperature of 45 degree Celsius.
“Within any city, there are pockets of temperature that are higher,” Mrutyunjay Mohapatra, the director-general at the India Meteorological Department, told The National. "This can be because of the urban heat effect but we are expecting some relief from today for Delhi as the temperature will likely drop to 41 degree Celsius."
Uttar Pradesh state's Banda district also recorded a high of 49 degrees Celsius, according to the IMD.
The weather office has warned of a continued heatwave in isolated pockets of Uttar Pradesh on Monday.
A dust storm and a thunderstorm is expected over northern parts of Punjab and Haryana.
The weather agency has advised people to not venture out of the house unless necessary and to drink sufficient water.
While the north was baking under the unprecedented heatwave, most parts of the southern peninsula experienced heavy rainfall.
The southern state of Kerala had 52.2mm of rain, while Lakshadweep recorded 57.7mm of heavy spells on Sunday.
A few low-lying areas in Kerala were flooded and state authorities deployed response forces and disaster management teams.
The weather office has issued a red alert — the highest level of warning — in five districts for heavy to very heavy rains on Monday.
It has urged people to avoid travelling to hilly areas prone to landslides and advised fishermen to avoid venturing into the sea.