India was battling on Wednesday extreme weather that caused severe heatwaves, landslides and floods, killing at least 11 people this week, among them a woman and her three daughters buried alive in a northeastern state, officials and media said.

The capital, New Delhi, sweltered through its hottest night in six years on Tuesday, with hospitals in the city of 20 million reporting at least five deaths from heatstroke this week, the Times of India newspaper said.

Floods and landslides triggered by incessant rain in the northeastern state of Assam killed at least six people on Tuesday night, officials said.

“A landslide buried a woman and her three daughters alive,” a state disaster management official, Siju Das, said by telephone.

"Their house was on a slope, and they died on the spot around midnight," he said, adding that the bodies were retrieved after a three-hour search operation by rescuers.

“A three-year-old was killed too.”

Billions across Asia are grappling with extreme heat this summer, in a trend scientists say has been worsened by human-driven climate change.

Since March, temperatures have soared to 50 degrees C (122 degrees F) in Delhi and the nearby desert state of Rajasthan, while more than twice the usual number of heatwave days were recorded this season in the country's northwest and east.

These conditions stemmed from fewer thundershowers, as well as warm winds blowing in from neighbouring arid regions.

In Assam, more than 160,000 people were affected, with waters surpassing the danger level in the Kopili, one of the largest tributaries of the Brahmaputra, which ranks among India’s biggest rivers.

More than 30 people in the state have died since the end of May in floods and landslides brought by heavy rain, officials said.