Questions over how an alternative Waitemata Harbour crossing in Auckland will be paid for.

Labour has announced a plan that includes two three-lane tunnels for vehicles and a 21 kilometre Light Rail tunnel between Albany and the CBD.

It'll take decades to finish and cost tens of billions of dollars.

NewstalkZB political editor Jason Walls says there's various ways of funding these types of projects.

"They come out of baselines within the Ministry of Transport, but there's also various other options. I mean, this week you've had the National Party talking about private capital, and obviously there's the debt option."

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