Updated 2.23PM: Auckland Mayor Len Brown says his hands are tied over Ports of Auckland's plans to expand into the Waitemata Harbour.

Dozens of the city's high profile residents have signed an open letter, saying the port's expansion is ruining the harbour views and congesting the harbour entrance.

Among them are Sir Stephen Tindall, Brad Butterworth, Chris Dickson, Lady Pippa Blake, Anika Moa and Neil Finn.

Yachtie Chris Dickson says enough is enough.

"It's turned from a harbour to a river. It's dangerous, it's unsightly, you can't take a little boat around that corner anymore because it's like a tidal rip. They're stealing a harbour to make a carpark."

Moa Brewing CEO Geoff Ross is among the sportspeople, business leaders, artists and academics who are endorsing the letter.

He says the city can do better.

"Do it in a better way. There are parts of the Port that can be better used to give Aucklanders access to the Harbour, and look a hell of a lot better than it is, which is a pretty poor caryard at the moment."

Boaties in particular are angry at the prospect of the narrowing of the harbour in order to let the Port park cars unloaded from container ships.

Expansion work starts next month and it's planned that three hectares of seabed will be added over time.

There's a protest about the moves at Queen's Wharf on Sunday.

Brown says a study on the port's place in the city is imminent but there's no way he can be drawn on a personal opinion.

"It is quite critical that I not give preferential views on consents that have been given and secondly how we will deal with rules as we're going through arbitration and mediation on Unity Plan rules right at this time."

Brown is calling for people on either side of the debate to enter a robust and mature discussion.