"A staggering number of workers are already being exposed to climate change-related hazards in the workplace and these figures are only likely to get worse," the UN' International Labour Organization said in a report.

Farm workers and others who carry out heavy labour in hot climates especially "may be exposed to a cocktail of hazards", the ILO said.

These hazards include excessive heat, UV radiation, air pollution, vector-borne diseases and agrochemicals.

Those working in hot indoor environments or poorly ventilated spaces are also at risk.

"Workers are among those most exposed to climate change hazards yet frequently have no choice but to continue working, even if conditions are dangerous," the report said.

It pointed out that in 2020 -- the last year for which statistics are available -- 2.4 billion workers, or more than 70 percent of the global workforce, were estimated to be exposed to excessive heat at some point.

That marks "a clear increase", Manal Azzi, the ILO's senior specialist on occupational safety and health, told reporters in Geneva.

The number of exposed workers had ballooned by 35 percent over two decades, and even adjusting for the growing global population, the percentage of the labour force affected had swelled by 8.8 percent since year 2000, she said.

- 'Huge issue' -

"This is a huge issue," Azzi said, warning that "workers are often forgotten when we're talking about climate change, and the health impacts are very severe".

Nearly 23 million occupational injuries attributed to excessive heat are reported each year, costing, on estimate, nearly 19,000 lives annually.

And those numbers do not include the more than 26 million people who live with chronic kidney disease linked to workplace heat stress, the ILO said.

Furthermore, the impact of global warming on workers goes well beyond heat exposure.

The report noted that numerous dangerous health conditions in workers had been linked to climate change, including cancer, cardiovascular disease, respiratory illnesses, kidney disfunction and mental health conditions.

The ILO said 1.6 billion workers worldwide were estimated to be exposed to UV radiation each year, with more than 18,960 work-related deaths annually from non-melanoma skin cancer.

Another 1.6 billion people were likely to be exposed to workplace pollution, resulting in up to 860,000 deaths among outdoor workers annually.

More than 870 million agricultural workers are meanwhile likely to be exposed to pesticides, with more than 300,000 deaths attributed to pesticide poisoning each year.

And 15,000 work-related deaths each year are attributed to exposure to parasitic and vector-borne diseases, the report said.

"It's clear that climate change is already creating significant additional health hazards for workers," Azzi said in a statement.

"It is essential that we heed these warnings. Occupational safety and health considerations must be become part of our climate change responses -- both policies and actions."

The ILO said climate change hazards could require countries to re-evaluate existing legislation or create new regulations to protect workers properly.

The agency will next year host an expert meeting with representatives of employers, labour and governments to discuss the issue, with the aim of coming up with fresh policy recommendations, Azzi said.