Orange's air quality still remains hazardous at lunchtime on Monday, with a rating of 903.

Armidale and the Northern Tablelands is currently battling the poorest air quality in NSW, though, with a rating five times that of a normal hazardous rank.

Armidale's sitting at 1042.

UPDATE: 11am

The air quality in Orange is still one of the worst in NSW, with the 875 measure well above the 200 mark used to indicate hazardous air quality on the NSW Planning Industry and Environment website.

EARLIER: 8.30am

Orange has the worst air quality in the state with a health warning issued to residents.

On Monday morning the numerical air quality rating for the city was 1294 which ranks as 'hazardous' on the NSW Department of Planning, Industry and Environment (DPIE) website.

That's the highest rating of any region across NSW.

"People with heart or lung disease, older adults and children should avoid exercising outdoors," the DPIE alert states.

"Everyone else should avoid prolonged or heavy exertion.

"If you have symptoms rest and use your reliever medication. If symptoms persists seek medical advice."

In the early hours of Monday morning a March Street business was engulfed by flames. That fire is now under control.

Meanwhile, the largest bushfire burning in the region is the Gospers Mountain fire which has reached 309,607 hectares and is listed as being controlled.

Stay up-to-date with fires in your area at Fires Near Me.