The Department of Conservation is calling for caution in Tauranga Harbour where it says there's at least one great white shark residing, and likely more.
Marine technical advisor Clinton Duffy said there had been a reasonable number of confirmed and unconfirmed sightings and captures of sharks in recent weeks.
"It is not unusual for them to be there, however when we're visiting the ocean, we need to be a little bit vigilant and aware of what's happening around us. Swim where there are surf lifesaving patrols, and don't swim or dive alone."
People visiting Tauranga Harbour over the long weekend are being advised to avoid swimming in the main channels, or berleying from kayaks and jet skis when fishing.
In one incident, Duffy said a jetskier was towed behind a berley bag by a shark.
He suggested people think twice about fishing off kayaks or jetskis in the harbour.
Duffy said people should also be aware great whites are a protected species and need to be released if they are caught.
Other species of shark protected in New Zealand include the basking shark, the oceanic whitetip, the small tooth sandtiger (deepwater nurse shark) and the whale shark.
Sightings, captures or strandings can be reported to DOC on 0800 362 468.