Bill English is still out in front in the preferred PM stakes, just.

The lead has changed again in the latest political poll but the election is on a knife edge.

The Newshub Reid Research poll puts National on 43.3 per cent, its lowest level in that poll in 10 years.

Labour is on 39.4 per cent up 6.3 on the previous month.

NZ First on 6.6 per cent and the Greens on 6.1 per cent are the only minor parties above the 5 per cent threshold.

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Labour leader Jacinda Ardern and National leader Bill English are deadlocked as preferred prime minister, with English just ahead on 30.1 per cent to Ardern's 29.9.

DAVID WHITE/STUFF Jacinda Ardern on the campaign trail on Sunday.

The result is reflected in an update to Stuff's rolling poll of polls, which has Labour edging ever closer to National. The poll of polls tallies the results of three published polls to smooth out any statistical blips that can show up in one-off polls.

The results come ahead of the second televised leaders debate between Ardern and English on Three on Monday evening.

Neither was a clear winner in their first debate on TV One last week.

The highly anticipated Stuff leaders debate on Thursday will pit them together in a town hall style debate.

The Three poll follows a bombshell 1 News poll last week that put Labour ahead of National for the first time in more than a decade. That poll had Labour at 43 per cent, ahead of National on 41 per cent.

On Thursday night Labour leader Jacinda Ardern said she was "surprised" by the results, and while they were "heartening" she wasn't taking anything for granted.

TOM LEE/STUFF Support for Winston Peters is falling, if polls are to be believed.

On Friday, speaking in her home electorate of Mt Albert, Ardern confirmed Labour's internal polls did not have her party ahead of National.

While Labour's polls had the party tracking up, it didn't reflect the same jump the Colmar Brunton poll displayed.

It's understood Labour's internal tracking polling has both parties neck and neck both slightly above 40 per cent.

Meanwhile, it's understood Nationals' internal polling has them still in the lead but with Labour closing.

"It is heartening for us, we are moving in the right direction, but as I said last night, the Colmar Bruton poll did surprise me. We're not taking anything for granted," Ardern said.

Ardern said despite the positive poll result there was a lot of hard work ahead, adding that poll results were changeable.

"Ultimately, there's only one that counts, as the cliche goes."

English has also said National's internal polling did not match the Colmar Brunton results.

National's polling is believed to show Labour polling around 39 while National is polling in the 40s.

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