It will be a test of the country's grit and resilience as a whole.
The Prime Minister could have added that this is also the biggest test of resolve and organisation National has faced in government since the 1951 waterfront strike.
It could even be argued National is grappling with New Zealand's biggest peace-time crisis since the Great Depression of the 1930s.
It is certainly the biggest challenge to confront Mr Key during his tenure as prime minister.
It has long been the case that this year's general election is one for a reasonably competent National Party Government to lose, rather than generally uninspiring Labour Party to win. The Christchurch earthquake has confirmed the veracity of that statement.
The enormity of what has happened to Christchurch has effectively turned Election Day into Judgement Day. And judgement will be made largely on one criterion - the adequacy of National's response to the quake.
Its handling of what promises to be a lengthy aftermath to New Zealand's darkest day will be the measure of its competence, plain and simple.
Since 12.51pm on Tuesday, normal politics have been in abeyance. There was no appetite for that this week - even among its more hard-nosed practitioners. Parliament sat only briefly - and then only to express solidarity with the people of Christchurch.
Notably, for the third time in six months, Labour's efforts to gain traction had come to a grinding halt, the other occasions being the first Christchurch earthquake last September and the Pike River mine explosion.
John Key was starting to sweat a bit over those now notorious BMWs. A dreadful tragedy has got him off the hook. It might be crass to say he was lucky, but that's politics.
Likewise, it was Phil Goff's constant bad luck to be marginalised once more until the necessary interval has passed in terms of showing respect for the dead.
The current political hiatus only benefits one person - the Prime Minister. Mr Key has been omnipresent, if not omnipotent. He has used the advantage of incumbency to maximum effect in terms of being in the public eye and hogging the media.
But he needs to do so.
He faces a huge task.
However, resurrecting Christchurch's economy from the forlorn-looking piles of bricks and fallen masonry strewn across the city could pay National a handsome electoral dividend - perhaps even enough seats to rule on its own, though Mr Key has indicated he will still try to run a governing arrangement with support parties as insurance for 2014, when National will likely struggle to maintain its support at current levels.
Failure could see National shed votes like confetti, however.
Contrary to reputation, the city is not the solid Labour territory it once was. National may hold only one of the city's six electorate seats.
Crucially, however, National secured a higher party vote than Labour in those seats - around 89,000 to 79,000. The former figure represents about 8.5% of National's nationwide party vote - a not insubstantial amount.
The smart move might be to adopt a bipartisan approach to hastening Christchurch's recovery - a move which would tie Labour down, but allow National to claim much of the credit if those recovery policies bear fruit.
But Mr Key has shown no sign of being interested, even though consensus on a special levy to meet what will be substantial costs in helping Christchurch get back on its feet might have been politically useful for National as a supposedly low-tax party.
Instead, ministers and officials are feverishly working on an emergency package of assistance for the city's residents and businesses to tide them over until a more specific plan for long-term recovery can be put in place.
The package's priority is to stop low morale in Christchurch starting to undermine what little economic confidence there remains across the rest of the country. That is why Mr Key has been so assertive in stressing Christchurch will be rebuilt. Its demoralised citizens must be persuaded the city has a future.
If the first quake last September left the city dazed, then Tuesday's bout almost delivered the knock-out punch. Almost.
The city (fortunately) was not razed. But it now faces the prospect of serious economic decline. The widespread damage to buildings and the city's infrastructure is going to make it hard for normal commerce to function.
Small and medium- sized businesses may judge it better to cut their losses than struggle on, knowing there might always be another Big One just around the corner which will see them kiss the linoleum once again.
The big question is whether anyone will be willing to invest money in the city, given that in the current economic climate, there is already risk aplenty.
The nation's focus this week has been on the search for survivors in the central business sector. But National's fate may hinge on what is happening in the suburbs.
Tumbling house prices, the damage to prized personal assets, the damage to infrastructure and the high possibility of losing one's job may fuel an exodus from of the city.
National has one thing going for it. It got a practice run last September in how to deal with the demands imposed by an earthquake.
However, the problems flowing from Tuesday's shake are exponential in comparison. The city's residents are tired and increasingly fed up. With the best will in the world, things go wrong, don't happen or don't work.
Much rests on Gerry Brownlee as the Earthquake Recovery Minister. But Mr Key will ultimately be the one calling the shots. He has already had to bang bureaucratic heads together to try and bring common sense to the release of victims' names.
There is also a drastic need to get someone with real communication skills to close the increasing divide between what is happening and what Civil Defence thinks people should be allowed to know what is happening. Not a very good start, given the stakes are so high for National.
• John Armstrong is The New Zealand Herald political correspondent.
