At least 15 people have died of suspected heatstroke in India's eastern states of Bihar and Odisha on Thursday, authorities said, with the region gripped in a debilitating heatwave expected to continue until Saturday.

India has been experiencing a blisteringly hot summer and a part of capital Delhi recorded the country's highest ever temperature at 52.9 degrees Celsius (127.22°F) this week, though that may be revised with the weather department checking the sensors of the weather station that registered the reading.

While temperatures in northwestern and central India are expected to fall in the coming days, the prevailing heatwave over east India is likely to continue for two days, said the India Meteorological Department (IMD), which declares a heatwave when the temperature is 4.5 C to 6.4 C higher than normal.

The deaths of 10 people were reported in the government hospital in Odisha's Rourkela region on Thursday, authorities told Reuters, while five deaths were reported in Bihar's Aurangabad city due to "sunstroke".

"About seven more people died on their way to the hospital yesterday but the exact cause of their death will be known after the autopsy," Aurangabad District Collector Shrikant Shastree told Reuters.

The Odisha government has prohibited outdoor activities for its employees between 11 a.m. and 3 p.m. when temperatures peak.

Three people died of suspected heatstroke in Jharkhand state, neighbouring Bihar, local media reported.

In Delhi, where high temperatures have been causing birds and wild monkeys to faint or fall sick, the city zoo is relying on pools and sprinklers to bring relief to its 1,200 occupants.

"We have shifted to summer management diet, which includes a more liquid diet as well as all the seasonal fruits and vegetables which contain more water," Sanjeet Kumar, director of the zoo, told news agency ANI.

Delhi, where the temperature is expected to touch 43 C on Friday, recorded its first heat-related death this week and is facing an acute water shortage.

Billions across Asia, including in India's neighbouring Pakistan, have been grappling with soaring temperatures- a trend scientists say has been worsened by human-driven climate change.

India, which is holding its national elections amidst the heat, is the world's third-biggest greenhouse gas emitter but has set a target of becoming a net-zero emitter by 2070.

While heat is affecting some of the country, the northeastern states of Manipur and Assam have been battered by heavy rainfall after Cyclone Remal, with several areas inundated on Friday.

Monsoon rains also hit the coast of the country's southernmost Kerala state on Thursday, two days earlier than expected.