Whale-spotters counted a record 23 whales in Cook Strait on Friday, the most sighted on one day since the annual survey began.
An early-morning fog lifted about midday allowing former whalers, Conservation Department staff and volunteer whale-spotters to watch Cook Strait unhindered through binoculars.
The group were gathered in a hut on the hill above Okukari Bay on Arapawa Island, Queen Charlotte Sound.
About 60 whales have been spotted so far in the ninth annual Cook Strait Whale Survey, which started on June 9.
It will run for another fortnight as part of efforts to assess the recovery of humpback whale numbers since the end of commercial whaling in New Zealand in 1964.
Volunteers spend every day from dawn to dusk counting the number of whales passing through Cook Strait as they make their annual migration north, from feeding in Antarctic waters to breeding and birthing in the South Pacific.
Joe Heberley, a whale spotter and former whaler, said the spotters had seen a rare spectacle of 11 whales, in different locations, at one time. "The previous best for the survey was 11 in one day, and we had them all at once and kept counting."
Mr Heberley, who has been part of the annual surveys since they began in 2004, said he had never seen so many whales at one time or in one day on the survey.
"The fog cleared about midday and there were whales in all directions.
"It was a real treat because we've had a couple of real crook days at the start of the week where we couldn't see anything and sometimes just sat out there in the hut and froze."
The whales were very active, splashing the water with their tails, which made them easy to spot.
"There's been a lot of whales breaching, popping up out of the sea. A pod of three were playing on the surface.
"They're real easy to follow when they do that."
The whale-spotters were in good spirits and held high hopes that this year's survey would beat last year's record of 73.
"Everyone's really happy, and we are only just halfway through the survey. We're on a real high note."
- The Marlborough Express