But while it used to be said that when the US sneezed, New Zealand caught a cold, Mr Key said America's economic wellbeing was no longer as crucial.
"We might have a sniffle but it's not going to be full-on influenza as it would have been a few years ago.
"New Zealanders should take confidence from the fact that we are structurally in a much more sound situation than either the US or Europe. We have much lower levels of debt, and higher levels of anticipated growth and we've taken a very conservative approach in our Budgets.
"Our unemployment data is good and our growth data is looking strong. We've got a couple of domestically focused events in the shape of the Rugby World Cup and the Christchurch rebuild that will support our economy irrelevant of what's happening internationally."
New Zealand was also fortunate to have strong markets in Australia and now China "to insulate against what's happening in our traditional markets".
Fonterra chief executive Andrew Ferrier said his company and other food producers were placed to withstand the turmoil.
"We're fortunate to be in the food industry, because the food industry is much more recession-proof than other industries, and it showed its way through 2007, 2008," he told TVNZ's Q+A yesterday.
"But we're not immune to economic volatility, and I think with the downgrading of the US, it's another sign that we are in very uncertain times, and in uncertain times you're going to see our kiwi dollar move around quite a bit, and both exporters and importers are going to get hit by that."
NZX chief executive Mark Weldon said unlike the 2008 global financial crisis, where confidence was lost across all financial markets, these problems were far more contained in the US and Europe.
"I'm not at all worried about Asia and interestingly Asia's gone now from being the growth engine of the world economy to the stabiliser so its role has become relatively more important in this."
Mr Weldon said New Zealand businesses were generally sound with many having reduced debt levels in the last three years.
But there was potential for the problems to spread to other financial markets, including those that New Zealand banks still relied on for part of their funding.
"The cost of funds is going to go up again, the duration that markets will lend for will go down. It means you're more likely to see interest rates start to go up independently of the [Reserve Bank's] official cash rate at some point."
Last week, Finance Minister Bill English noted the Reserve Bank has put in place measures to strengthen the banking system and was ready to prop up banks with short-term cash to banks in the event of another crisis.
Tony Hildyard, the New Zealand boss of giant global bond investment manager Pimco, said unlike 2008 the current turmoil was a "market pricing correction" rather than a failure of large parts of the system.
He expected the New Zealand dollar to fall a little lower, interest rates to increase and global growth prospects to drop a little, but it would be a temporary setback.
Market sources were unwilling to predict what the current turmoil would mean for oil and petrol prices.
