John Key's preferred prime minister rating in the latest Newshub/Reid Research poll is at its lowest point since he took office - but National's party support has held steady.

Labour leader Andrew Little has not fared well either - getting the support of just 8.9 per cent of the population as preferred PM, a drop of 1.5 per cent.

Mr Key's support in the poll is at 36.7 per cent. In January last year he was riding higher at 44 per cent.

But National held its support at 47 per cent. If poll results were translated to seats in Parliament, it and its support partners Act (0.4 per cent), the Maori Party (1 per cent) and United Future (0 per cent) would fall one seat short of the 61 needed to put together a government.

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Labour fell 0.9 per cent to 31.3 per cent, with the Green Party rising by the same margin to 11.1 per cent.

New Zealand First would hold the balance of power, having polled 7.8 per cent - a result that would give it 10 seats.

Leader Winston Peters also received a boost in the preferred prime minister polling - rising 2.8 per cent since the last poll to 12.1 per cent.

The Newshub/Reid Research poll has a margin of error of 3.1 per cent.