At least seven people have died in India's southern state of Kerala after heavier than normal pre-monsoon rains, authorities said, even as much of South Asia grappled with a heatwave.

Pre-monsoon rains were 18% above normal in Kerala this year, causing flooding in parts and disrupting flights at the Kozhikode airport, officials said.

According to the state's Disaster Management Authority (KSDMA), a 70-year-old man died in a lightning strike in Kasaragod district on Wednesday, while brothers aged 18 and 21 died after falling into a quarry filled with water in Palakkad on Tuesday.

Four people also died in Idukki and Pathanamthitta districts after falling into water, said an official at the SDMA.

The local weather department has issued a red alert, warning of extremely heavy rainfall in three districts on Thursday.

In contrast to Kerala, most of India and Pakistan faced heatwaves, with India's capital New Delhi ordering the closure of schools earlier this week.

Temperatures often peak during May, but India's weather department was predicting seven to ten heatwave days in northwestern regions this month, compared to the usual two to three days.

New Delhi will vote on Saturday, along with the nearby states of Haryana and Uttar Pradesh among others, in the penultimate phase of a seven-stage national vote, with temperatures predicted to touch 46 degrees Celsius (115 Farenheit) on the day.

In neighbouring Pakistan, authorities advised people to stay indoors and avoid non-essential travel, as temperatures were predicted to go beyond 48 C in some parts.

"The soaring temperatures across South Asia can put millions of children’s health at risk if they are not protected or hydrated," the U.N. children's agency UNICEF said.

Extreme temperatures in Asia have been made more likely from human-driven climate change, international scientists said earlier this month.

(Reporting by Jose Devasia in Thiruvanathpuram and Mubasher Bukhari in Lahore, Ariba Shahid in Karachi; Writing by Shilpa Jamkhandikar; Editing by Andrew Cawthorne)