Large parts of northwest India broiled in extreme heat for a second consecutive day on Saturday, with temperatures surpassing 45 degrees Celsius in many places.
Parts of Madhya Pradesh and Gujarat also experienced a heatwave.
The brutal heat scorching northwest India will continue for another five days, with Delhi, Haryana, Punjab, Rajasthan and Uttar Pradesh likely to bear the maximum impact, according to the India Meteorological Department (IMD).
The Met office has issued a "red" warning for Delhi, Haryana, Punjab and west Rajasthan, stressing the need for "extreme care for vulnerable people".
It has issued an "orange" alert for east Rajasthan, Uttar Pradesh and Bihar, and emphasised "high health concern" for vulnerable people, including infants, the elderly and those with chronic diseases.
At least 20 places in Delhi, Punjab, Haryana, Rajasthan, Uttar Pradesh, Gujarat and Madhya Pradesh recorded maximum temperatures of 45 degrees Celsius or above.
In Delhi, Mungeshpur recorded a high of 46.8 degrees Celsius, Najafgarh 46.7 degrees Celsius, Pitampura 46.1 degrees Celsius and Pusa 46 degrees Celsius.
Temperatures breached 46 degrees Celsius at four places in Rajasthan: Jaisalmer (46.2), Barmer (46.9), Ganganagar (46.3) and Pilani (46.3).
The Met office said high humidity could add to people's inconvenience in Goa and sub-Himalayan West Bengal over the next few days.
The IMD also said warm night conditions are likely in Uttar Pradesh, Bihar and west Rajasthan over the next two to three days.
High night temperatures are considered dangerous because the body does not get a chance to cool down. Increasing night-time heat is more common in cities because of the urban heat island effect, in which metro areas are significantly hotter than their surroundings.
In view of the ongoing general election in India, experts have warned of an increased likelihood of heat-related illnesses in people exposed to the sun for prolonged periods or engaging in heavy work.
Researchers at Climate Central, a US-based group of climate scientists, said 543 million (54.3 crore) people in India will experience at least one day of extreme heat between May 18 and May 21.
"Human-caused climate change has made this intense heat much more likely. The high overnight temperatures make this event particularly alarming," said Andrew Pershing, vice-president for science at Climate Central.
Heatwaves can be deadly, with the elderly and children particularly at risk of heat exhaustion and heatstroke.
According to the World Health Organization (WHO), more than 1.66 lakh people died as a result of heatwaves between 1998 and 2017.
Extreme temperatures can also impact economies. People are less productive during hot weather, even if they work indoors, while children struggle to learn in extreme heat.
A 2022 study said extreme heat resulted in a labour productivity loss equivalent to USD 2.1 trillion in 2017.
On Friday, the maximum temperatures surged to 47.4 degrees Celsius in Najafgarh and 47.1 in Haryana's Sirsa.
Before this, Kalaikunda in the Gangetic West Bengal region had recorded a high of 47.2 degrees Celsius on April 30.
The threshold for a heatwave is met when the maximum temperature of a weather station reaches at least 40 degrees Celsius in the plains, 37 degrees Celsius in the coastal areas and 30 degrees Celsius in the hilly regions, and the departure from normal is by at least four-and-a-half notches.
A severe heatwave is declared if the departure from normal exceeds by 6.4 notches.
April witnessed record-smashing maximum temperatures in the east, northeast and peninsular India, prompting health warnings from government agencies and leading a few states to suspend in-person classes in schools.
Union minister Nitin Gadkari fainted due to heat while addressing an election rally in Maharashtra, while a television host fell unconscious during a live broadcast in West Bengal.
Several places recorded their highest-ever April day temperatures, with the mercury soaring to 47 degrees Celsius. At least two people died in Kerala due to suspected heatstrokes during this period.
On Wednesday, a group of leading climate scientists said similar heatwaves could occur once every 30 years and these have already become about 45 times more likely due to climate change.
The scientists from the World Weather Attribution group emphasised that heatwaves intensified by climate change are making life much tougher for people living in poverty across Asia.
The IMD had earlier warned of extreme heat in India during the April-June period, coinciding with the seven-phase Lok Sabha election that ends on June 1.
