The sighting of two large sharks at Orewa have closed the beach.
Auckland Council's SafeSwim website says the shark sightings were reported at 3.30pm and swimming was not advised.
The alarm was raised after the police Eagle helicopter spotted the sharks' shadows from above.
A police spokeswoman said one of the sharks was about 200m offshore while the other was further out.
The police then reported it to the local surf lifesaving club.
Shark expert Scott Tindale said it was likely the sharks were bronze whalers which were very common and tended to be closer to shore at this time of year.
The young sharks come in to feed on fish and generally shy away from the public.
"And as the temperature rises, more people are out on the water so are more likely to see them which is why we get more sightings this time of year," Tindale said.
"But they're always there."
Sharks up to 2-3m long have been spotted at two North Shore beaches in recent days - one close to the city.
Around 11am on Boxing Day lifeguards at Orewa Beach in northern Auckland confirmed a 2m shark had been spotted by multiple paddleboarders as close as 150m from shore, according to RNZ.
The beach was closed until 3pm, and swimmers were urged not to use nearby Red Beach or Hatfields Beach.
The shark was also spotted on Christmas Eve, about 500m offshore.
In the evening on Christmas Day the police maritime unit advised that a 2-3m shark was spotted in Browns Bay, also on Auckland's North Shore.