Binoculars and cameras were out as about 50 people watched the baleen whale frolic about halfway between the Esplanade and White Island for at least an hour before noon.
Department of Conservation marine technical adviser Hannah Hendriks confirmed the whale was a southern right whale, or tohora.
Over summer, southern right whales go offshore and feed, while over winter they go to socialising and nursery grounds, primarily near the Auckland Islands, she said.
"Some of them come to the mainland where people can get a really good chance of seeing them because they often come really close to shore and might even look like they are going to strand, but they don’t.
"Sometimes they scratch their bellies on the sea floor."
Historically, before whaling, the slow, acrobatic swimmers bred in harbours throughout New Zealand.
Doc hoped increasing sightings around the mainland might mean breeding began here again, she said.
Southern right whale populations suffered dramatic losses due to whaling as they were deemed the "right" whales to catch.
The whales were easy to approach, lived close to shore and provided large quantities of meat, oil and baleen.
Both southern and northern right whale species were hunted nearly to extinction.
