The Department of Parks and Wildlife has issued a smoke alert for the Perth Hills, Dwellingup and parts of the south-west including Collie and Donnybrook.
The smoke is from a number of prescribed burns carried out on Friday for nature conservation and to manage bushfire risk.
The smoke from the prescribed burn 12km south of Collie is impacting on Collie-Preston Road in the Shire of Collie.
The road has been reduced to one lane. For further road closure information contact Main Roads on 138 138.
The smoke from prescribed burns 10km south-east of Mundaring and 25km east-south-east of Jarrahdale will also be highly visible to motorists travelling on Brookton Highway in the Shire of Beverley and Albany Highway in the Shire of Wandering.
Smoke may reduce visibility and motorists should take care, turn on headlights and travel at appropriate speeds when travelling in these areas.
The smoke is expected to remain visible in the Perth Hills and Dwellingup areas, and between Collie and Donnybrook for several days.
If the smoke is particularly thick, it is recommended people shut doors and windows and turn off air-conditioners.
People with asthma and pre-existing respiratory or cardiovascular illnesses should follow their pre-prepared treatment plan.
People with conditions exacerbated by smoke should take precautions in line with their medical advice for these circumstances.
More information on prescribed burns can be found at www.dpaw.wa.gov.au/todaysburns OR www.dpaw.wa.gov.au/news/alerts