Residents in north Nelson have reported seeing large whales in Tasman Bay.
They believe they were either southern right or humpback whales.
Rosemary Cooke, who has lived in the area for 35 years, said while they regularly saw dolphins and Orca, she had not seen whales as large as this before.
Local boaties said Tasman Bay has been full of krill in recent days, which is a primary diet for both whale species.
"We could see out by the corner marker of the marine reserve, some whales breaching and some spouting. It looked at first as if there was one, and then possibly two whales," she said.
Project Jonah general manager Daren Grover said it was unusual, but not unheard of, for the whales to be in Tasman Bay at this time of year.
"Humpbacks are migratory and are usually seen in winter, heading up to the tropics.
"These could have been stragglers on the way back, and the food might have brought them in - they might have taken a detour into Tasman Bay on the way through Cook Strait," Mr Grover said.
Otago University zoologist and researcher Liz Slooten said, from the descriptions, they could have been either humpbacks or right whales.
Dr Slooten said sperm whales tended to stick to their home territory around Kaikoura rather than migrate.
There were blue whales in Cook Strait, not far from Tasman Bay. Sightings of humpbacks and right whales were becoming more frequent as populations recovered.
"It's not particularly exceptional, but they probably wouldn't normally come so close people could see them from their houses," Dr Slooten said.
Local surfer Mark Nichols said the whales were grey and up to 10 metres long.
He said they were 500 metres to a kilometre offshore and were "big".
"We saw Orca a couple of weeks ago and we could tell they weren't those. We also saw them spouting. I did see a right whale at Wharariki (West Coast, below Farewell Spit) a couple of years ago and these looked similar. My four-year-old, who's a bit of an expert, reckoned they were humpbacks."
In June, a rare Brydle whale and its calf were filmed feeding off the Auckland Coast.