Temperatures in India's capital soared to a national record-high of 52.3 degrees Celsius (126.1 Fahrenheit) on Wednesday, the government's weather bureau said.
The India Meteorological Department (IMD), which reported "severe heat-wave conditions", recorded the temperature in the Delhi suburb of Mungeshpur on Wednesday afternoon, smashing the previous national record in the desert of Rajasthan by more one degree Celsius.
The temperature was more than 10 degrees higher than expected, the second day of record-breaking heat, and pushed up the mercury by more than degree from the 2002 record of 49.2C (120.6F).
The IMD has issued a red alert health notice for the city, with an estimated population of more than 30 million people.
The alert warns there is a "very high likelihood of developing heat illness and heat stroke in all ages", with "extreme care needed for vulnerable people".
India is no stranger to searing summer temperatures but years of scientific research have found climate change is causing heatwaves to become longer, more frequent and more intense.
- 'Waiting for the monsoon' -
But people on the streets of Delhi said there was little they could to do avoid the heat.
"Everyone wants to stay indoors," said snack-seller Roop Ram, 57, adding he struggled to sell his savoury fritters.
Ram, who lives with his wife and two sons in a cramped house, said they had a small fan but that did little to cool them down.
They were counting down until the rainy season arrives in July.
"I am not sure what else we can do to cope," he said. "We are just waiting for the monsoon."
Rani, 60, who uses only one name, travels by bus for two hours each morning to sell jewellery to tourists at a makeshift street stall.
"It is definitely hotter, but there is nothing we can do about it," she said, gulping water from a bottle she brought from home.
"I try to refill the bottle from anyone around."
Heat remains high even at night, the IMD said, noting that the temperatures were "likely to reduce gradually" from Thursday.
- 'Water scarcity' -
New Delhi authorities have also warned of the risk of water shortages as the capital swelters in headache-inducing heat, cutting supplies to some areas.
Delhi Water Minister Atishi, who only uses one name, said supplies had been halved in many areas to boost flow to "water-deficient areas".
Atishi on Wednesday ordered state authorities to "immediately deploy 200 teams" to crackdown construction sites or commercial properties using domestic pipes to stem a "serious wastage of water".
Delhi relies almost entirely on water from neighbouring Haryana and Uttar Pradesh, both farming states with huge water demands.
The highly polluted Yamuna river, a tributary of the Ganges, runs through Delhi but its flow is hugely reduced during the summer months.
- Cyclone kills 65 -
Many blame the soaring temperatures on scorching winds from Rajasthan state, where temperatures on Tuesday were the hottest in the country at 50.5C (122.9F).
Rajasthan's desert region of Phalodi holds India's all-time heat record of 51C (123.8F) hit in 2016.
Neighbouring Pakistan has also sweltered through a week-long heatwave, which peaked at 53C (127.4F) on Sunday in Mohenjo Daro in rural Sindh province.
Pakistan's meteorological office said it expected temperatures to subside from Wednesday but warned further heatwaves were coming in June.
It comes as Pakistan hashes out a new deal with the International Monetary Fund that is believed to focus heavily on an energy supply crisis that has left parts of the country facing up to 15 hours of load-shedding a day.
At the same time, India's West Bengal state and the northeastern state of Mizoram are recovering after a cyclone hit India and Bangladesh on Sunday, killing at least 65 people.
Bangladesh's Meteorological Department said the cyclone was "one of longest in the country's history", blaming climate change for the shift.