Greens co-leader hopeful Chloe Swarbrick is vowing to grow the party's caucus until it's big enough to lead the Government.

The Auckland Central MP has announced her candidacy to replace James Shaw - who resigned this week - and will step back in March.

Swarbrick told Heather du Plessis-Allan she sees herself contributing to a movement which turns the Greens into the major left party.

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