The whale that's been attracting attention in Wellington Harbour has stolen the show, causing the postponement of tomorrow's Matariki Sky Show until next weekend.

Wellington's acting Mayor, Jill Day, said the postponement call was made this afternoon following advice from the Department of Conservation and mana whenua amid concerns over public safety on the water.

"The advice we've received is that the noise from the fireworks is unlikely to cause harm to the whale but that it could cause it to act unpredictably if it is in the vicinity," Day said.

"We don't want anyone in boats or kayaks on the water, in the dark, to come off second-best if the whale breaches among them.

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"We also don't want the whale to be injured in any contact with a vessel."

The southern right whale has been putting on a show in the harbour for the past five days, causing a stir on social media and among the capital's residents with its frolicking, despite getting in the way of the Interislander ferry.

"Hopefully by next weekend the whale will have departed the inner harbour and headed to Petone or Eastbourne or out into Te Moana-o-Raukawa [Cook Strait]," Day said.

She said there had been strong iwi and public sentiment in favour of a postponement.

"Wellingtonians have fallen in love with this whale – this taonga - and they've been telling us they don't want anything untoward to happen to it. The whale's presence is a true blessing for Matariki."

She said the council would be talking during the week to interested parties, including the Harbourmaster, iwi and police, about how to deal with the situation if the whale is still in the harbour next weekend.

"We think we can find a solution that enables us to celebrate our harbour visitor – and watch a stunning fireworks display."

Department of Conservation [DOC] marine species threats manager Ian Angus said experts from DOC and the University of Auckland were consulted to determine what the risks to the whale were, their significance, and if they were possible to mitigate.

"Our primary concern is increased vessel traffic, including risk of vessel strike and increased underwater noise from vessels.

"Our experts' opinion is that the noise of the actual fireworks will be significantly muted underwater and is unlikely to harm the whale."

He said DOC appreciated there was a keen public interest in the welfare of the southern right whale.

"We made some suggestions to WCC around whale location, vessel restriction and responsible boating behaviour to minimise the vessel traffic risk."

These included monitoring the whale's whereabouts, limiting the number of vessels in main, on-water viewing locations if the whale was confirmed to be near, reducing vessel speed and applying extra caution, and maintaining the required legal distances.

"Not only is there a risk to the whale from vessels, there is also a risk to smaller vessels, and non-motorised vessels especially, if the whale is breaching which it has been seen to do over the past few days."

Angus said the whale was spotted this morning near the Interislander Ferry Terminal, but there was still no reason to believe that its behaviour was unusual or it was under any duress.

"We do want to reiterate that whale watchers need to keep at least 50m away from the whale and no more than three vessels and/or aircraft should be within 300m of any marine mammal. 'Vessel' includes boats and kayaks."

The Matariki Sky Show would now go ahead next Saturday, or if it rains, Sunday.