Prime Minister Jacinda Ardern has rocketed up as preferred Prime Minister in the latest poll and Labour has also climbed but the National Party was rock solid under the onslaught.

Ardern soared up to 38 per cent support as preferred Prime Minister in the latest Newshub Reid Research poll - up 8.3 points since the last poll following news she was pregnant and the Government's first 100 days in power.

The poll had National on 44.5 per cent, the same as its election night result.

Labour was fast catching up to National as the end of its first 100 days in government drew to an end - it was on 42.3 per cent, more than five points above its election night result and its highest result in that poll since 2007.

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Ardern said she was pleased there had been a good reception for the start of the new government but would not rest on her laurels.

"It's certainly encouraging but I'm also mindful people will be giving me the benefit of the doubt in the early days and I just need to keep proving that this team is going to make a difference."

The poll was released on a day in which the first serious speculation circled about the leadership team of National leader Bill English and his deputy Paula Bennett.

English's support as preferred PM had dropped to 25.7 per cent, down nine points since the last poll. However, there was a vote of confidence in his handling of the job of leader of the Opposition – 53 per cent of those polled said he was performing well or very well in his job.

Only 24 per cent said he was performing poorly and 20 per cent were neutral.

The big casualty was NZ First. Its support had almost halved since its election night of 7.2 per cent to just 3.8 per cent – well below the five per cent threshold to get into Parliament.

On the poll results, NZ First would be out of Parliament but Labour would be able to form a government with the Green Party. The Green Party was steady on six per cent and will be hoping that the attention on its upcoming leadership contest will help give it a boost.

Peters has frequently blamed National for its election night result being lower than hoped, saying Bill English's call for voters to 'cut out the middle man' was responsible and prompted National leaning voters to abandon NZ First for National.

Peters was at 5.7 per cent as preferred PM, down 1.4 points since the last poll.

The poll also asked whether Ardern's pregnancy would improve or diminish her performance as Prime Minister.

Thirty four per cent said it would improve her performance, 39 per cent said it would have no effect, and 20 per cent said it would worsen her performance.​

The Newshub-Reid Research poll was of 750 people interviewed by phone and 250 online between January 18 and 28.

The margin of error is +/-3.1 percent.