The intense smoke and dust from the catastrophic bushfires has hit global mining giant BHP's east coast coal operations, with newly installed chief executive Mike Henry saying air quality has been affected and the company is "monitoring the situation".

Production from BHP's NSW coal division, which is used to power electricity, decreased by 11 per cent in the December quarter as a result and also because of a strategy to focus on higher quality products.

Production from BHP's NSW coal division decreased by 11 per cent in the December quarter. Credit:Nic Walker

"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 company said.

In an update ahead of reporting its half-year results on February 18, the miner said guidance for its 2020 energy coal production remained unchanged at between 15 million and 17 million tonnes.