New Zealand is officially in a recession - the harshest, sharpest, and deepest on record - but Prime Minister Jacinda Ardern says she's focused on bouncing back.   

"It's actually about the rebound and I back New Zealand's rebound. I think we're already seeing that we were able to open up a lot more quickly, we're seeing activity picking up," she said on Thursday. 

Recession hits with two consecutive quarters of negative growth, and the latest - which takes into account 43 days in alert levels 3 and 4 - saw GDP fall to 12.2 percent. 

"The economic damage was recorded in three months but the consequences will last for many, many years to come," said National's finance spokesperson Paul Goldsmith. 

Finance Minister Grant Robertson says the recession is purely the before and after shot of COVID-19.

"There is no way that any political party could claim that there would not have been a recession in New Zealand during this period of time. This is a one-in-100-year global economic shock," he said. 

Recessions are hitting the world over. The UK's economy fell by 20.4 percent, the US by 9.1 percent and our closest cousins in Australia are down 7 percent. 

"I back our approach," Robertson said. "I think we compare well with Australia on a number of fronts, and I think we'll see that as time goes on."

National Party leader Judith Collins says her party "absolutely" would have handled it better and that the economic situation would be different.  

She pointed to the fact that construction sites were forced to put down tools during the lockdown which meant activity in the sector declined by 26 percent. 

"It just beggars belief that that sort of pragmatic but principled approach was not taken. There was a better way and the Government failed to take it," Collins said. 

As bad as it is - i.e. the worst it's ever been - it still could've been worse, leaving a much nastier taste. 

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In May's Budget, Treasury was predicting a drop in GDP of 23.5 percent, and on Wednesday when the Government's books were opened, it revised that down to a 16 percent drop. 

"Economic forecasting is always more of an art than a science," Robertson said. 

It wasn't the only thing Treasury got wrong. The all-important PREFU book detailing the Government's accounts - handed out to journalists and economists - was, in fact, the wrong draft with the wrong numbers. 

"Treasury has got sloppy under Grant Robertson's watch," Goldsmith said. 

National also pointing to last year's botched Budget when Treasury accidentally posted parts of it online which was obtained via a search function.  

"As a country, we're in a deep hole at the moment and we need a really strong economic plan to get back on our feet," Goldsmith said.

Analysis by Political Editor Tova O'Brien 

National is presenting its alternative budget on Friday, its economic plan and costings for all its campaign promises, and included in that is new tax policy. 

National has been getting a lot of grief from Labour for not properly costing its policies and spending up large. Robertson has become fond of calling the party irresponsible and chaotic when it comes to the economy. 

So Friday is all about National trying to reclaim the economic higher ground that it has traditionally held. 

As for the political damage a recession will do to Labour so close to an election, it certainly doesn't help, but in terms of apportioning blame, COVID-19 is so exceptional that it makes for a pretty good excuse.