Climate change is having an unprecedented negative effect on human health, the World Health Organization announced in a new report on Tuesday.

The document, released on the second day of the UN Climate Summit (COP25), homes in on the growing health threat from pollution, extreme weather, and mosquito-born diseases. It called on governments to hit challenging targets to cut heat-trapping carbon emissions in an effort to save millions of lives.

During a news briefing, Maria Neira, director of WHO's department of environment, climate change and health said: "Health is paying the price of the climate crisis. Why? Because our lungs, our brains, our cardiovascular system is very much suffering from the causes of climate change which are overlapping very much with the causes of air pollution."

She added it was "absolutely outrageous" that less than one percent of financing, put aside for combating climate change, ended up in the health sector.

"WHO considers that climate change is potentially the greatest health threat of the 21st century," said WHO expert Diarmid Campbell-Lendrum.

"Unless we cut our carbon emissions, then we will continue to undermine our food supplies, our water supplies and our air quality - everything that we need to maintain the good health of our populations," he added.

Some 101 countries have acknowledged the WHO's survey on the threat of climate change, although several of the world's biggest polluters, including India and the United States, are yet to respond to the health body on the issue.

Campbell-Lendrum said: "Over two-thirds have assessed that they have increased risks from heat stress, from injury and death from extreme weather, from food, water and vector-borne diseases and those range from everything from cholera to malaria." 

The WHO estimates that more than seven million people a year die from air pollution.