Wellington Police are reminding whale-watchers they cannot stop their cars on the motorway to try to catch a glimpse of the city's "celebrity mammal".

People have taken to parking up on the motorway shoulder over the past few days after a rare southern right whale made itself at home in the Wellington Harbour.

Excited locals have been flocking to the waterfront to watch the whale, which has been playfully breaching in the harbour since Tuesday, when it was first spotted.

But some people are choosing unsafe places to stop for a look.

"We understand that people are keenly interested in viewing our special harbour visitor, and we certainly don't want to stand in the way of that," a police spokesperson said.

"However we do need people to be safe about it and we have had several near-misses on the motorway already today."

"So please, if you are out and about for a bit of whale-watching today, head to a designated parking spot before getting out of the car."

The presence of the whale has caused tonight's Matariki fireworks display to be delayed until next week, because the show could cause the whale to behave unpredictably - harming itself or people out on the water.

Some online commentators say the whale's presence is a more appropriate celebration of the Matariki festival than a fireworks display.

Although it has been delighting onlookers, the whale has been causing a bit of trouble for the Interislander ferry, which has had to delay berthing on some occasions.