Motorists can expect delays on Old Windsor and Abbott Roads, Baulkham Hills, as Fire and Rescue NSW fight a bushfire threatening houses.
Two south-bound lanes have been closed and police are advising to avoid the area.
Residents have been commenting about the smoke on The Hills LAC Facebook page.
"That explains why my house is full of smoke," posted Amanda Hughes-Kevric.
Rebecca Bugeja said: "Bit close for comfort; hope it is contained quickly."
Earlier today, firefighters put out a fire on the median strip on Norwest Boulevard near the intersection of Windsor Road about 12.30pm.
The west-bound lane was closed by police and Fire and Rescue NSW who contained the fire which caused traffic delays in both directions.
On the Hills police Facebook page residents theorised on the cause of road fires.
Among the police responses was the following: "Unfortunately Lauren you would be surprised by the number of motorists that throw their cigarette butts out the window."
It has been a busy start to the bushfire season for Fire and Rescue NSW and the Rural Fire Service.
The RFS has attended up to 70 fires across the state today in extremely windy conditions.
#NSWRFS firefighters are gaining the upper hand on the 69 fires burning across NSW. All fires are currently at Advice level.— NSW RFS (@NSWRFS) October 1, 2013