Mining giant BHP has said Australia's horror bushfire season is taking a toll on its coal production.

On Tuesday, the company said energy coal production in New South Wales fell 11 per cent to seven million tonnes for the second quarter, partly blaming the fires.

Management reported in their first-half trading update that work had slowed due to poor visibility in December, when the fires were at their worst and some employees took leave to protect their homes.

AAP

BHP management was wary of the crisis continuing.

"We are monitoring the situation and if air quality continues to deteriorate then operations could be constrained further in the second half of the year," the report read.

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At least 28 people have died as fires swept large areas of Australia over recent months.

But some were quick to slam BHP by highlighting the connection between fossil fuels and climate change, which has been linked to the crisis.

"You can't make this stuff up! Coal production down because of air quality as the result of #AustraliaFires," actor Terry Serio said on Twitter.

You Can't Make This Stuff Up! Coal production down because of air quality as the result of #AustraliaFires

A spokesman from #BHP warned that coal production could drop further unless air quality improved @ABCNewsRadio #ScottyfromMarketing #LiarFromTheShire #lnpcorruption #auspol — 💧Terry Serio (@TerrySerio) January 21, 2020

Last year, UNSW professor Jeremy Moss pointed out the extent of BHP's emissions.

"BHP's emissions from its global fossil fuel operations alone were more than the whole of Australia's domestic emissions (534Mt CO₂-e) for 2018," he wrote.

"If BHP were a country, the products it produces would cause emissions greater than those emitted by 25 million Australians."

Additional reporting: AAP