Allan Mundy, Surf Life Saving New Zealand's national search and rescue manager, told Morning Report the increase in sightings was understanding, given conditions at beaches.
"We are seeing more sharks than probably what we would normally see," he said.
"But if we have a look at what is actually happening on the beach, we've got clear water at the moment, there hasn't been a really big swell, so the visibility in the water is really good and we are seeing a lot more people down on the beach, walking and swimming, because of the Covid effect."
The fact sharks were being spotted along the coast shouldn't cause alarm as the predators - mostly bronze whalers and thresher sharks, according to lifeguard reports - were simply cruising and not feeding, he said.
"They're pretty much doing what we would be doing, enjoying the warm water, basking and cruising. There's not any real food source along the surf beaches.
"These sharks feed out to sea or in the harbours where there's lots and lots of food ... If they're hunting, they are in stealth mode."
He said if a shark was sighted while swimming the most important thing to do was not panic, but to get calmly out of the water and alert others in the general vicinity.
"Look to where your whānau is, gathering them. If you feel uncomfortable, make your way back to shore at best pace, but don't panic by any means. What that will do is, you're more likely to lose members of your family out the back, or get disorientated."
He said beachgoers should share the information with those close by, but they shouldn't go around clearing the entire beach.
"Take a note of the direction of the shark and you might want to inform those downstream more, but again, don't panic."
Department of Conservation marine scientist Clinton Duffy said people should exercise caution by always swimming between the flags, never swim alone at a non-patrolled beach and avoid swimming at night, and where people are or have been fishing.
Mundy said it had been a quiet summer in general for lifeguards so far, with calm conditions and very little surf.
"We're getting massive crowds and people are sticking between the flags, so I think we're getting a combination of public support - helping us to help them - and calm conditions, and that's why we haven't seen a massive number of rescues."
