Light rail linking Wellington's central train station to the airport would be built by 2027, under Green Party policy announced tonight.

A fully-electric bus fleet would also be introduced to Wellington by 2030 under the Green Party's transport policy for the capital.

The light rail line would run separate from traffic, from the train station to Newtown by 2025 and to Kilbirnie and the airport by 2027.

The line would cost between $630-700 million, depending on the route, the party said.

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"Light rail will transform Wellington by making the city a quieter, more people-friendly space and allow thousands of people to travel quickly to work, back home again and beyond," leader James Shaw said, speaking at Wellington's Paramount Theatre.

"The Greens will provide a one-off investment of between $30-50 million to upgrade underground trolley bus infrastructure, rather than wasting money pulling down the near-new overhead wires and converting trolley buses to diesel-hybrids."

The Greens last night announced an 11th hour decision to stand Tane Woodley as an Ohariu candidate, after United Future leader and Ohariu MP Peter Dunne announced he was quitting the contest.

Wellington is a strong voting base for the party and they need all the support they can muster after one recent poll put them below the 5 per cent threshold needed to return to Parliament.

Last month the Greens pledged to build light rail between Auckland Airport and the CBD in time for the America's Cup in 2021.

Labour leader Jacinda Ardern has announced policy to build a 20km light rail line from Auckland CBD to the airport as a priority, partly funded by higher petrol prices.

National announced transport policy this month to build 10 major highways around the country if it remained in power after September, including four-lane highways between Auckland and Whangarei.