More than 100 fires remained active across NSW on Wednesday night, with two - Carrot Farm Road at Deepwater and Crown Mountain south of Glen Innes - at the watch and act alert level.

Meanwhile the NSW Rural Fire Service confirmed 724 homes, 49 facilities and 1,582 outbuildings had been destroyed and 2.7 million hectares burned over the fire season.

The crisis motivated thousands to rally for climate change action in Sydney, with protesters at Town Hall on Wednesday night brandishing signs reading: "Denial is not a policy", "Less debate more climate action", "For my grandkids" and "Climate change is a public health emergency".

Earlier, NSW Environment Minister Matt Kean reiterated the fires were linked to climate change, after coalition colleague Sarah Mitchell said the bushfire debate was "philosophical" and Emergency Services Minister David Elliott labelled it "unpalatable".

"This should be a debate of science, this should not be a philosophical debate ... the majority of scientific opinion is very clear on this fact," Mr Kean told ABC radio.

"We've got to stop making climate change a matter of religion and we've got to start making it a matter of science and the science says that we need to reduce the impact of global warming by 2C and in order to do that we need to get to net-zero emissions by 2050."

Premier Gladys Berejiklian later said her government accepted the reality of climate change but she stopped short of linking it to the bushfires.

Mr Elliott appeared to change his tune saying: "I agree with what the premier just said."

Sydney's air quality remained hazardous in the southwest and poor in the northwest Wednesday night as smoke from fires lingered, yet it was good in the city's east.

The overall air quality forecast for Thursday is fair.

There will be total fire bans in place on Thursday for northwestern NSW and the northern slopes where the danger will be severe.

It will be very high in the central ranges, southern slopes, New England and eastern Riverina.

Australian Associated Press