The air quality index is only fair in Gunnedah, but in Narrabri it's poor and Tamworth it's hazardous, according to Office of Environment and Heritage data this morning.

Gunnedah residents who are unusually sensitive to air pollution are being urged to consider "reducing prolonged or heavy outdoor exertion", and Narrabri residents with heart or lung disease to limit exercising outdoors.

In Tamworth, adults and children - especially those with heart or lung disease - are urged to "avoid outdoor exertion and stay inside as much as possible".

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Meanwhile, the situation is not set to improve, as planned back-burning in Mount Kaputar National Park fire will mean residents in the area may see an increase in smoke.

Fire crews are planning to strengthen the containment line along the Scutts Hut fire trail, and will also back-burn south of Pound Rock in an effort to contain some spot fires that occurred recently.

They will continue to patrol and monitor the fire burning to the west of Mount Lindesay Road and Wirrawee Road.

Yesterday, fire activity increased north of the Amore Hills property and in the Lindesay area west of Mount Lindesay Road and Wirrawee Road.

Firefighters, supported by aircraft and heavy machinery, were able to manage the situations in those locations and prevented the fire breaching containment lines.

Firies also back-burnt along the Foggy Dell north fire trail south towards Upper Bullawa Creek Road, to establish containment in that part of the fireground.

Firies from the Rural Fire Service (RFS), National Parks and Wildlife Service and Queensland Fire and Emergency Service, supported by aircraft and heavy machinery, are focused on taking advantage of favourable conditions.

This is in order to build and strengthen containment lines around the fire perimeter ahead of unstable weather predicted from Friday.

There is no total fire ban in effect today, but a very high fire danger rating for Gunnedah, Narrabri and Tamworth.