Crews on Sydney's North Shore were responding to reports of smoke when they spotted a civilian drone hovering over the area.

Although no fire was found, the drone could have seriously hampered firefighting efforts, the Killara rural fire brigade said in a post on Facebook.

"If a fire was confirmed at the location we would not be able to request any aerial assistance due to the sighting of a drone near the fire," the brigade posted in a statement on Facebook.

"Please do not fly drones near fires, you are risking lives, if you fly then we can't."

The Killara brigade also saw a number of vehicles coming to "sightsee" whether there was a fire.

"This not only causes traffic congestion but also slows down our ability to respond," the RFS crew said.

"Don't drive to where the fire trucks are going."

NSW RFS spokesman Matt Sun said the use of drones on fire grounds was a "highly dangerous practice" for the public, firefighters and air crews.

"If there are drones in the areas we are forced to ground aircraft for safety reasons and obviously when those aircraft are grounded that means they're not responding to the fire," Mr Sun told AAP on Tuesday.

Civil Aviation Safety Authority spokesman Peter Gibson said flying a drone near a bushfire was illegal.

The act could attract fines of up to $10,500 and prosecution may be sought where people are put at risk, Mr Gibson said in a statement on Tuesday.

"There are no circumstances where an unauthorised drone should be flown near a fire," he said.

"It is sheer stupidity as it puts lives at risk, both on the ground and in the air.

"A mid-air collision with a firefighting aircraft could be catastrophic."

Mr Sun said people shouldn't be seeking out dangerous areas.

"People shouldn't be going out of their way to try and get photos of these situations, they shouldn't be anywhere near the bush at all, it is that dangerous," he said.

Australian Associated Press