The National Party is on just 29 percent, while Labour is polling at 55 percent, according to the latest survey by Labour's pollster.
There's been recent speculation around the leadership of National's Simon Bridges, with some MPs worried about his ability to hold the party vote up to the levels it was polling before the Covid crisis struck.
Under his leadership National's party vote had been holding up well, generally in the low to mid forties.
In early February the Newshub Reid Research poll had National on 43 percent with Labour on 42; a week later the 1 News Colmar Brunton they were on 46 and 41 respectively.
The leaked UMR poll shows a big jump for Labour, driven by the government's handling of the Covid-19 crisis and in particular the role played by Prime Minister Jacinda Ardern.
It was done during the final stages of level 4 lockdown and has Labour on 55 and National dropping to 29.
It has polled New Zealand First at 6, the Greens at 5 and ACT on 3.
National MPs have told RNZ they haven't been given any detailed internal polling for a few months.
When asked about that earlier this week Bridges said the caucus discussed polling periodically but he was not prepared to talk about internal polling with the media.
In a statement to RNZ, a spokesperson for Bridges UMR said Labour's pollsters and are "consistently, badly wrong".
"Labour should focus on getting New Zealand back to work not leaking dodgy numbers", they said.