Greater Auckland says travel times of less than 90 minutes between Hamilton and Auckland and under 60 minutes between Hamilton and Tauranga would link more than half the country's population.
It would allow for journeys that were faster than driving and skip the traffic completely. A revitalised train network would also stitch the economy of Auckland, Hamilton and Tauranga with the benefits of growth and development in the main centres spilling over into nearby towns and villages.
The final stage would see lines extending across the Waikato and Bay of Plenty.
"National has let regional rail services rust away but the Greens in government will restore rail as the backbone of New Zealand's transport system, for freight and for people," said Green Party transport spokeswoman Julie Anne Genter.
"I expect a lot of people from Hamilton and Tauranga will be attracted by the idea of being able to work and rest while on the train, and avoid Auckland traffic once in the city.
"There's been a lot of talk about passenger rail to Hamilton. We now have a plan to make this happen in our first term in government."
She said a journey was expected to take about 2.25 hours between Auckland and Hamilton and 3.5 hours between Tauranga to Auckland.
Genter said a trial would cost $20 million over five years.
"If this trial is successful, we'll look at creating a premium, fast service that would be about an hour quicker. This is estimated to cost around $400 million and could start in 2025."