Labour's Jacinda Ardern has leapfrogged over her leader Andrew Little to get 10.5 per cent as preferred Prime Minister in the first poll since she became deputy leader.

The Newshub Reid-Research poll has Little on 8.3 per cent - down two points since the last Reid Research poll last year while Ardern was up by almost 8 points to 10.5 per cent.

Neither were close to Prime Minister Bill English on 25 per cent while NZ First leader Winston Peters was on 8.9 per cent. And 52 per cent of voters believed English was performing well - far outnumbering the 17 per cent who said he was not performing well.

That compared to 35 per cent who said Little was performing well while 36 per cent said he was performing badly.

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The poll was taken from March 10 - 19 - a period in which Ardern was getting significant attention after being appointed deputy to replace Annette King.

Little - who has struggled to break into double figures in the polls - told Newshub he was not worried about Ardern's popularity and it was "not awkward".

At the time she was elected deputy, Ardern insisted she would not overtake Little in the polls - repeatedly saying "it's not going to happen".

The poll follows English's announcement of a plan to lift the retirement age from 65 to 67 from 2037. ​

That did not appear to have damaged National, which saw its support climb two points to 47.1 per cent while Labour dropped back to 30.8 per cent.

The Green Party had inched up slightly to 11.2 per cent - but even with NZ First (7.6 per cent) Labour would fall one seat short of being able to form a Government.

National was also one seat short of being able to form a Government with its current three partners and would need NZ First.

The remaining parties all polled less than one per cent - including Gareth Morgan's The Opportunities Party which debuted at 0.8 per cent.

The poll of 1000 voters had a margin of error of +/- 3.1 per cent. About one quarter of respondents were from an internet panel.