Severe heat has left dozens dead over a 24-hour period in India's Bihar state, as the country enters the third week of searing temperatures, officials said on Sunday.

The deaths occurred in three districts of the poor northern state, where temperatures have hovered around 45 degrees Celsius [113 Fahrenheit] in recent days, senior health official Vijay Kumar told AFP.

Forty-nine people died in three districts of the Magadh region that has been hit by drought, he said. "It was a sudden development on Saturday afternoon. People affected by heatstroke were rushed to different hospitals," Kumar added.

“Most of them died on Saturday night and some on Sunday morning during treatment.”

Kumar said about 40 more people were being treated at a government-run hospital in Aurangabad.

“Patients affected by heat stroke are still being brought, the death toll is likely to increase if the heatwave continues.”

Most of the victims were aged above 50 and were rushed to hospitals in a semi-conscious state with symptoms of high fever, diarrhoea and vomiting. Twenty-seven people died in Aurangabad district, 15 in Gaya and seven in Nawada district, officials said.

State Chief Minister Nitish Kumar has announced a compensation of 400,000 Indian rupees [$5,700] for the family of each victim.

Harsh Vardhan, India's health minister, said people should not leave their homes until temperatures fall. “Intense heat affects the brain and leads to various health issues,” he said.

Large parts of northern India have endured more than two weeks of sweltering heat.

Temperatures have risen above 50 degrees Celsius [122 Fahrenheit] in the desert state of Rajasthan.

A heatwave in 2015 left more than 3,500 dead in India and Pakistan.

In 2017, researchers said South Asia, which is home to one-fifth of the world's population, could see heat levels rise to unsurvivable levels by the end of the century if no action is taken on global warming.