National has risen above 50 per cent again in the latest 3 News political poll, while Labour and the Greens polled 43 per cent between them - well short of the majority needed to form a government, even if the Maori Party and Mana leader Hone Harawira sided with Labour.

After successive polls showed a Labour-Greens bloc was gaining ground on National, in the 3 News Reid Research poll National was on the rise again to 51.4 per cent, while both Labour and the Greens had dropped two points since last November - Labour to 32.6 per cent and the Green Party to 11 per cent.

David Shearer's support as preferred Prime Minister had also slipped from almost 13 per cent to 10 per cent, while Prime Minister John Key's increased slightly to 41 per cent.

However, there were some glimmers of hope for Mr Shearer, who beat Mr Key in one area: only 20 per cent believed Mr Shearer was out of touch with "ordinary people" compared to 52 per cent who believed Mr Key was.

About 35 per cent of voters said he was performing well as leader of the Opposition and 48 per cent believed he was a capable leader.

The proportion of voters who rated Mr Key as performing well had dropped from 68 per cent in November 2011 to 57 per cent.

No other parties made it over the 5 per cent threshold: NZ First came closest on 3.4 per cent, the Conservative Party was on 0.9 per cent, the Maori Party on 0.4 per cent, United Future on 0.3 per cent, and Act on 0.1.

The Mana Party was on zero.

The Reid Research poll of 1000 voters was taken from February 12-21 and has a margin of error of 3.1 per cent.

Meanwhile, Prime Minister John Key believes New Zealanders would be more open to having a four-year electoral term than they were when the idea was voted down in public referenda in 1967 and 1990.

Mr Key has said the country would benefit from a four-year parliamentary term but the change needed to be supported by the public via a referendum.

The proposal failed when it was put to voters in the 1967 and 1990 elections, with almost 70 per cent favouring the three-year term over four years.

Mr Key told TVNZ's Breakfast this morning that there could be a different outcome if it went to a referendum now.

"Twice in New Zealand's history we've voted on a four-year term. Both times it was rejected roughly two thirds [to] one third but I think the mood's definitely changing with MMP."

He said 2017 was the earliest we would see a four-year term introduced.

"My view of it is we hardly ever have one-term governments in New Zealand. Three years, whether you love or hate the colour of the government that's in office at the time, is a bit too short to properly assess them, and actually elections are expensive and slow the process down, so four years would be better than three."

The Labour Party and United Future both support the proposal of a four-year term, while the Greens and New Zealand First have acknowledged the merits of the idea.

- APNZ