Authorities in Australia have started deploying shark-spotting drones at popular beaches which have already led to the evacuations of two school groups swimming near an eight-foot creature.

The drones – painted in red-and-yellow stripes to match the well-known uniform of Australia’s life guards - are being used at five beaches across Perth in the state of Western Australia, where there has been a spate of shark attacks in recent years.

The state’s life guard association said the drones have been deployed for two weeks and have already come to the aid of beachgoers.

Chris Peck, from Surf Life Saving Western Australia, said a drone spotted a shark on two occasions at Secret Harbour, a beach in the south of Perth.

The most recent sighting was of an eight-foot shark on Monday, though the species was not identified.

"Our drone patrol at Secret Harbour during a routine patrol has picked up a shark off the back of a break on Monday morning," Mr Peck told Fairfax Media.

"It was about … 100 metres off-shore, swimming in a zig-zag pattern. There were about 20 surfers in the water at the time and two school groups with about 30 kids in each. So the drone is a great benefit from a localised surveillance perspective... we're able to take immediate action."