The closure of Birubi Beach on Monday and again on Tuesday during the school holiday period meant the evacuation of hundreds of beachgoers during the hottest part of the day.

On Monday, the NSW Department of Primary Industries aerial team on board the helicopter spotted a 1.25 metre shark off Samurai Beach at about 11.48am.

The beach was evacuated. Just 14 minutes later quite possibly the same shark was spotted off Birubi Beach, forcing the evacuation of swimmers and surfers.

Then on Tuesday, a NSW Surf Lifesaving drone detected a 1.5 metre shark (of unknown species) off Birubi Beach just before 2.30pm, forcing another evacuation of the beach.

Phil Rock, the Port Stephens Lifeguard supervisor, said that the sighting of sharks was a result of more eyes in the sky, not necessarily because of an increase in the number of sharks.

"With the support of DPI helicopters and drones it stands to reason that we are going to get more shark sightings off our beaches," he said.

A DPI spokesperson said that beaches would be evacuated if there was a potential of a dangerous shark lurking in the waters.

"If the pilot spots a shark that poses a threat to surfers or swimmers, a call is immediately made to the local surf lifesaving club. The helicopter will reduce its height to hover, a siren will be sounded, and beach authorities are notified."

The most recent shark attack in Port Stephens occurred at Samurai Beach on October 21 last year, when a 50-year-old man enjoying a morning swim was bitten by what was believed to be a bull shark.