Auckland Mayor Phil Goff expects a new harbour crossing will be ready by mid-2030, as the current bridge faces days of repairs. 

Work could begin to temporarily fix Auckland's Harbour Bridge over several nights from tomorrow evening.

The four middle lanes are closed, causing big delays this morning - and doubling and tripling some journeys to the city.

NZTA's Brett Gliddon says a strut damaged on Friday will be repaired with a new section of steel, which has arrived from Taranaki.

He says the work could take up-to three nights - but they won't know until they start the job.

Southbound lanes will close from 9pm to 5am from tomorrow until the repair's complete.

Goff says that the temporary repairs will make a big difference.

In terms of a longer term solution, Goff says that work is underway now to look at another harbour crossing. 

He told Heather du Plessis-Allan it's a Transport Agency project that will likely cost more than $8 billion, and will likely be more than that.

"Obviously it's a big job because it's not just putting the tunnel under the harbour, it's aligning the roading at both ends - and that's even if it is roading." 

Goff says that he has been told that construction won't begin until the end of this decade.

"When you are talking about spending $8 billion, you want to make sure they've got it right. And then you've got the problem that, wherever you put the tunnel out, it will be disruptive," citing that people's properties will be affected by a new corssing. 

Goff says no one can be blamed for the current situation, given it was wind that the