People affected by the Port Hills fire - including firefighters who helped control it - are being offered free doctors' visits.
Civil Defence in Christchurch said about 100 firefighters were working to ensure there were no flare-ups from hotspots and control the remaining 10 percent of the fire perimeter.
It said this work might create dust or smoke, and strong winds might also blow dust from the area towards properties.
Civil Defence said the dust might irritate eyes, noses and throats or worsen pre-existing respiratory illnesses.
It said people should close their windows and doors, and avoid going outside in the smoke if they could.
Free GP visits are available for those affected until 13 April.