If the polls are a seesaw, National Party leader Simon Bridges is on the seat going down while NZ First is in danger of being crushed underneath.

The latest poll out is 1 News Colmar Brunton's poll and is very similar in movement to the Newshub Reid Research poll taken in late January. It shows National down on last year - and Labour up, and ahead of National.

In the 1 News poll, National and Labour are both back to where they were in October last year with Labour a couple of points ahead of National. December's poll showed National rising from 43 to 46 and Labour dropping from 45 to 43.

National is now back down to 42 - a chunky four point drop from December - and Labour is again up on 45.

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Such seesawing between the two has been going on in the Colmar Brunton poll since the 2017 election.

And when the two major parties are in a close race, it only brings bad news for the smaller parties. So NZ First has dropped further to just 3 per cent - around the same as in the Newshub poll.

In such circumstances, it will come as a relief for the Green Party that they have managed to stick it out over the 5 per cent threshold, nudging to 6. That will also please Labour - it shows the "share" on the left is rising and the parties are not simply cannibalising each other.

Prime Minister Jacinda Ardern's rankings have now reached a high of 44 per cent. As was former Prime Minister John Key, she seems immune from any fallout from the daily slush of politics. The KiwiBuild kerfuffle and any wariness of a possible capital gains tax have not hurt her one jot.

On the other hand, Simon Bridges has simply gone down in every poll since he took over. He has plummeted from a high of 12 per cent in May to 6 per cent now. Worse, National has slipped to its worst poll result since the election.

It will inevitably feed into ongoing speculation about whether Bridges should be replaced. Bridges was seen to have a good start to the year after his announcement to adjust tax thresholds, and his promise to release policy discussion documents in short order.

The polls indicate the public is either deaf to him or not convinced.

The Colmar Brunton polling period began on February 9 and ended on February 13. The Newshub poll was released with a bang in the middle of that on the 11th and got a lot of traction.

Some in National see that as something of an excuse for the result in the 1 News poll.

Excuses will not get them far. The last time the polls between the two major parties were seesawing like this was in the two weeks before the 2017 election.

Then National managed to stall Ardern's rise in the polls, using attacks on tax policy and the so-called "fiscal hole" to do it. That shows it is possible to stop a trend.

However, that is a lot easier when you are the party in Government and there are no question marks over your leadership.

The seesawing indicates things are at the slippery sands stage of things for National. As previous Opposition leaders have found, slippery sands can all too quickly turn to concrete.