Jacinda Ardern has been elected unopposed as Labour's new leader after a caucus meeting following Andrew Little's decision to step down.

Kelvin Davis has been elected as deputy leader and is believed to be the first Maori to hold that post in the Labour Party.

It follows a turbulent week for Labour in which three polls puts its support in the low 20s - and Little stepped down from the job, saying he had to take responsibility for the result.

Little put Ardern in as his deputy in a bid to help raise Labour's fortunes, saying she appealed to the younger generation and was a valuable asset in Auckland.

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However, Ardern's polling as preferred Prime Minister swiftly overtook Little's own. In the latest Newshub Reid Research poll she was on 8.7 per cent to Little's 7.1 per cent.

She featured in most of Labour's campaign advertising.

On Sunday, Little had revealed he had raised the prospect of standing down with senior colleagues but they had urged him to stay.

The fallout from that admission effectively resulted in his decision to go.