With India and Pakistan reeling under an extreme heatwave, the countries are working to roll out life-saving health action plans, the UN weather agency has said.

The extreme heat is impacting hundreds of millions of people in one of the most densely populated parts of the world, threatening to damage whole ecosystems.

Working closely with health and disaster management agencies, the national meteorological and hydrological departments in both countries, plan to roll out heat health action plans, which have been successful in saving lives in the past few years, said the World Meteorological Organization (WMO) Friday.

Both India and Pakistan have successful heat-health early warning systems and action plans already in place, including those specially tailored for urban areas.

They reduce heat mortality and lessen the social impacts of extreme heat, including lost work productivity.

The India Meteorological Department said maximum temperatures reached 43-46°C in widespread areas on April 28, and this intense heat will continue until May 2.

Similar temperatures have also been seen in Pakistan, with daytime temperatures likely to be between 5°C and 8°C above normal in large swathes of the country, said the Pakistan Meteorological Department.

In the mountainous regions of Gilgit-Baltistan and Khyber Pakhtunkhwa, the unusual heat levels would accelerate snow and ice melt, with the possibility of triggering glacial lake floods or flash floods in vulnerable areas, it added.

Air quality has also deteriorated, and large swathes of land are at risk of fire outbreaks.

It is premature to attribute the extreme heat in India and Pakistan solely to climate change, said the WMO. "However, it is consistent with what we expect in a changing climate."

The Intergovernmental Panel on Climate Change, in its recent Sixth Assessment Report, said heatwaves and humid heat stress would be more intense and frequent in South Asia this century.

Also read: Deadly flooding, heatwaves in Europe, highlight urgency of climate action: WMO

The current heatwave was triggered by a high-pressure system and follows an extended period of above-average temperatures.

India recorded its warmest March on record, with an average maximum temperature of 33.1°C, or 1.86°C above the long-term average.

Pakistan also recorded its warmest March for at least the past 60 years, with several stations breaking March records.

In the pre-monsoon period, both India and Pakistan regularly experience excessively high temperatures, especially during May.

India has established a national framework for heat action plans through the national disaster management authority which coordinates a network of state disaster response agencies and city leaders, to prepare for soaring temperatures and ensure that everyone is aware of heatwave protocols.

The city of Ahmedabad in India was the first South Asian city to develop and implement a city-wide heat health adaptation, in 2013, after experiencing a devastating heatwave in 2010.

This successful approach was then expanded to 23 heatwave-prone states and serves to protect more than 130 cities and districts.

Pakistan has also made strides towards protecting public health from heat.

In the summer of 2015, a heatwave engulfed much of central and northwest India and eastern Pakistan and was directly or indirectly responsible for several thousand deaths.

The event acted as a wake-up call and led to the development and implementation of the Heat Action Plan in Karachi and other parts of Pakistan.

Typical plans make sure the targeted intervention is a right fit and designed for the heat vulnerable population of a city.

It first identifies the heat hotspots of the city, locates the vulnerable populations in these pockets, and assesses the nature and status of their vulnerability to extreme heat.