New Zealand First's plan to buy back the Bank of New Zealand is an "outlandish proposal", says an economist.

NZ First leader Winston Peters on Sunday announced a policy to automatically enrol all newborn citizens into KiwiSaver with a $1000 government contribution, alongside a proposal to buy back the Bank of New Zealand and merge it with Kiwibank to create a new state-owned bank.

Speaking at a campaign event at the Trusts Arena in West Auckland, Peters said the new entity - to be known as "National Bank of New Zealand" - would be commercially run and designed to compete more aggressively with the major Australian-owned banks operating in New Zealand.

Infometrics principal economist Brad Olsen said it "headline-grabbing" rather than "serious policy".

He argued there were little details as to how the policies would be carried out, which made it difficult to understand what effects they might have.