A bushfire burning at Risdon Vale in Tasmania's south has burnt about 375 hectares.
The fire started on Downhams Road at Risdon Vale about 2:30pm on Wednesday.
The Tasmanian Fire Service has 28 crews at the scene, including four helicopters.
The service says the blaze is burning in rugged terrain.
While it is not directly threatening properties, that could change for houses in King Road.
The service is warning of a build up of smoke in the greater Hobart area.
Police believe the fire was not deliberately lit.
Another bushfire at nearby Richmond has been contained.
The Asthma Foundation is urging people with respiratory illnesses to be vigilant as more fires hit the state.
Exposure to smoke can trigger symptoms such as wheezing, coughing, chest tightness or shortness of breath.
Cathy Beswick from the Asthma Foundation of Tasmania says if possible, sufferers should stay indoors and ensure medication is on hand.
If you can see the smoke ahead of you and it is visible and you are in amongst it and you can smell it and see it then it is getting deep down into your lungs and that is where it can be doing damage and usually once you are exposed the reaction can be quite instantaneous," she said.