A record-breaking “heat dome” across northwest India has worsened a severe shortage of coal for power generation and raised the risk of blackouts at hospitals in New Delhi, according to government statements.

The heatwave, which has pushed temperatures to more than 45C in places, is forecast to worsen this weekend and ease after May 2, according to the India Meteorological Department.

The high temperatures, which began in March, have driven up power demand from air conditioning units, worsening a critical shortage of the coal that is used to generate power for New Delhi and other nearby cities.

The intense temperatures, from 35 degrees in Mumbai up to 43 degrees in New Delhi, have arrived much earlier than usual, taking the country by surprise and exposing hundreds of millions of people to heat stress.

“We are seeing many cases of heat exhaustion, dysentery, body ache, and the number of viral fever cases has increased too since the last two weeks,” said Dr Madhav Thombre, a general practitioner based in Mumbai. “This year the heat was severe and came earlier than usual.”

The prolonged heatwave is caused by a stagnant weather pattern or “heat dome”, similar to the one that caused record heat and fires across Canada and the north-western US last year.

This March was the hottest March in more than a century in northwest India, and April is poised to set records too.

The stagnant weather that drives such a long heatwave is caused by a slowing of the jet stream, according to Zachary Zobel of the Woodwell Climate Research Center in Massachusetts. The jet stream is a fast-moving band of air high in the atmosphere that governs the weather patterns of the northern hemisphere.

As the world warms, heatwaves “are going to get more intense and occur over longer durations”, said Zobel. “There will be parts of the world that will be at times nearly uninhabitable. This is another piece in the data set that is trending in that direction.”