Several Southern Right whales are currently in the waters around Wellington, including what is believed to be a mother and calf in the harbour.
The Department of Conservation said there was also potentially another pair on the Kapiti coast.
DOC said it had not yet been able to determine if they are known whales.
It said people should stay at least 200 metres away from a whale and calf, further than the usual 50 metres stand-off distance for marine mammals.