They have dropped by 17 percentage points, the One News/Colmar Brunton poll showed.
Meanwhile, Labour is up to 59 percent, up 18 percentage points.
Jacinda Ardern's 63 percent as preferred Prime Minister is up 21 percentage points on the last poll. Opposition leader Simon Bridges, who faces a leadership challenge tomorrow at National's caucus by MP Todd Muller, was down 6 percentage points to just 5 percent.
And it's bad news for the Greens and NZ First, which are both below the 5 percent threshold.
Greens were at 4.7 percent and NZ First were on just 2 percent. Act was at 2 percent.
Despite the very low numbers, Bridges told One News he would not be stepping down. Bridges blamed the bad poll result on the Covid-19 crisis.
"We've seen this the world over in response to Covid where the Government gets a bounce and there's a situation where we've had wall-to-wall coverage of the Government and the PM."
He called the leadership challenge a "distraction".
"We will resolve that quickly and that means we can get back to the things that matter for New Zealanders."
He said he was confident ahead of tomorrow's leadership vote.
"I'm very confident tomorrow, but these are now things for the caucus."
The poll result is the worst for National in 15 years.
Looking at how the poll translates to seats in the House, Labour would be able to govern alone with no support partners.
They would have 79 seats in the House, compared with National's 38.
This means many current National MPs would lose their jobs and won't be returning to Parliament after the election.
Bridges blamed the bad poll result on the Covid-19 crisis.
The 1 News Colmar Brunton poll is the second public poll to be released this week following a Newshub Reid Research poll on Monday which sparked a leadership challenge against Bridges by Muller.
MPs have been summonsed back to Wellington in a recess week after Bridges called an emergency caucus at midday Friday to settle the matter.
In the Newshub poll, National dropped almost 13 points to just 30.6 percent while Labour rocketed up to 56.5 percent following Prime Minister Jacinda Ardern's handling of the Covid-19 crisis.
Tonight's poll was taken a week later, from Saturday May 16 until Wednesday.
A triple-whammy of events was in play: The post-Budget glow for the Government, the end of the Covid-19 level three days, and National's own leadership turbulence.
As Bridges contended with the leadership challenge, Ardern was on her first visit since the Covid-19 lockdown began, visiting Rotorua to promote the Budget's tourism package.
The poll is the first poll since the Budget when the Government announced a $50 billion Covid-19 response package, including wage subsidy extensions, state house construction plans and further help for sectors hit by the crisis.
The last Colmar Brunton political poll was taken before Covid-19 hit in February and had National in a position to secure the Government benches with the support of the Act Party. National was on 46 percent while Labour was on 41 percent.
Bridges was at 11 percent as preferred Prime Minister while Ardern was well above him on 42 percent.
