Transport Minister Michael Wood has unveiled five options for an additional Auckland Harbour crossing for Tāmaki Makaurau.
Watch Prime Minister Chris Hipkins and Transport Minister Wood answering questions about the announcement.
Construction of the long-awaited second Waitematā crossing is expected to begin before the end of the decade.
A final decision is scheduled for June, with construction to begin in 2029.
At the media briefing, Hipkins said: "I don't think there's going to be any shortage of political support for a second Waitematā harbour crossing. The key thing now is we've just got to get on and make sure that's going to happen."
He said the government knew from experience of dealing with multiple infrastructure projects, such as Transmission Gully, that they took a long time. The country has to lock in these projects, and the government was committed to this, he said.
Wood said: "Any project like this does have a significant construction period."
The length of the construction period would depend somewhat on which options were chosen.
In terms of Auckland's mass rapid transit network he wanted to look at the development of it and then stage pieces of it to allow "a really clear pipeline with the construction industry".
"A major project like this will be a significant investment in the billions of dollars," Wood said.
It would be shaped by the options chosen, and the government was also looking to develop a linked up network, Wood said.
"This is a city and nation shaping investment," Wood said.
"What people consistently tell us is that what we lack in Auckland is a proper linked up mass rapid transit transport public transport system - that is what we're building in this project," he said.
The government will work closely with Auckland Transport.
Overall tunnelling options were likely to take longer on the construction side, Wood said.
The costs and benefits of the options would need to be weighed up before making the best decision, he said.
Hipkins said the government had an emissions reduction plan that it remained committed to.
Major projects such as this one would require the contracting in of outside expertise, the prime minister said.
Cross party support wanted
He was confident there would be cross party support for it because National had made a commitment to a second harbour crossing at the last election.
The government formally wrote to National Party about the development of a mass rapid transport network in Auckland last year. It had followed that up a couple of times and hasn't yet received a formal response, Wood said.
Hipkins said every time an incoming government changed the plan it would result in more delays.
The government will keep working on getting National support, but at the same time won't be held back from making decisions, Wood said.
He said doing the work up front on what the best options are would be critical.
"The overall goal of this project is to give Aucklanders more transport choices, to reduce our emissions and to increase mode shift. There is no doubt in my mind that if we provide more efficient, high quality timely public transport to the North Shore more people will use it," Wood said.
On the timeframe of the project, Wood said: "The previous version of the Auckland transport alignment plan that the previous government put in place had work on this project commencing in the 2040s and the most recent version of ATAP that we issued a couple of years ago, we indicated the 2030s.
"Today's announcement confirms that we're bringing that forward by making a clear decision on the preferred route and mode by the middle of this year and commencing construction by 2029."
He said the date had been brought forward because the project was so critical for Auckland.
When asked about people living in the south of Auckland, Wood said that was why the project was not being advanced in isolation. It would link into Auckland light rail and investing in Drury and a third main line in southern rail lines.
There will be some disruption to communities but they would be supported, but the alternative of doing nothing was not an option because the transport situation would get worse, Wood said.
Persistent congestion hinders city's progress
In a statement earlier, Wood said Auckland businesses had made it clear that persistent congestion was one of the biggest barriers to the success of Auckland.
"We want an unclogged, connected, and futureproofed transport network so Aucklanders can get to work on time, and don't need to wake up earlier just to get their kids to school - it's vital that we have a harbour crossing that works for the city," he said in a statement.
Construction for the additional Waitematā Harbour connections would begin in 2029 and would provide a future-proofed solution for people wanting to get across Te Waitematā as fast as possible.
"After considering feedback from Aucklanders, we've developed five scenarios for future transport connections across Te Waitematā including both bridge and tunnel options. The scenarios also include ways to connect to growing residential and business hubs on the North Shore," Wood said.
A new walking and cycling link across the harbour is considered in each scenario, as well as a new light rail link to connect Auckland Light Rail in the city centre, he said.
Light rail is the key to building a linked up rapid transit network across the city and to providing "faster, safer, low-carbon travel", he said.
"A new rapid transit connection from the city centre to the North Shore will fully integrate with other projects including Auckland Light Rail and rapid transit to the Northwest to allow people to travel seamlessly across Auckland," Wood said.
Feedback provided would help shape the final decision on the preferred option which would be confirmed in June 2023, he said.