A thresher shark came within metres of swimmers, one of many sightings which have prompted lifeguards at holiday hotspots to urge caution.

Sharks have been seen at Bay of Plenty and northern beaches, some as close as a metre from shore. Large sharks have also been reported at Waihi, Papamoa and Omanu.

Surf Lifesaving Bay of Plenty said it was unlikely all the reports related to the same shark, as estimated sizes ranged between 1.8m and 2.5m.

All those seen in the bay were believed to be thresher sharks - identified by their long tails, small dorsal fins and slender bodies.

Omanu Beach head guard Leigh Sefton said he spotted one near swimmers and warned them of the danger.

"Although some swimmers removed themselves from the water, others swimmers and surfers remained as the shark moved past."

Surf Life Saving Bay of Plenty chief executive Sarah Lucas said the thresher sharks were acting suspiciously, at least from a human perspective.

"Maybe they were just being nosy. They were coming up close to swimmers and causing a bit of panic.

"Thresher sharks have a massive fin which shows above the water and can terrify people really, because it makes the shark look even bigger than it is."

Groups of bronze whaler sharks have reportedly been spotted close to shore at Omaha, Ruakaka and Waipu.

Holidaymakers at Mt Maunganui main beach were also treated to the sight of two orca frolicking 200m offshore.