Last month's trade deficit was an unexpectedly small $472 million as imports exceeded exports by 13 per cent.
Market economists had been looking for a deficit of $1.1 billion.
Trade flows are always in the red in August but the latest deficit compares with an average 24 per cent of exports over the previous five Augusts.
When adjusted for seasonal effects it was a surplus of $328 million, Statistics New Zealand said, boosted by higher volumes for exports of dairy products, meat, fruit and seafood.
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August last year recorded a trade deficit of $1.2 billion, but that included the importation of an oil rig and of $120 million more crude oil than last month, while the latest monthly balance also benefited from $100 million more of live animal exports.
The trade balance for the year to August 2014 was a surplus of $2 billion, up from an annual surplus of $1.25 billion in July as August 2013's large deficit dropped out of the annual total.
But while exports for the full year ended August at $51.3 billion were up 12.7 per cent on the year before, exports in the latest three months were up only 2.3 per cent on the same period last year.
Economists expect that slowdown to continue as falling dairy and forest product prices weigh on export receipts.
Imports were down 2.8 per cent on July in seasonally adjusted terms and down 11.8 per cent on August last year, or 7.9 per cent when the oil rig is excluded.
Imports of consumer goods were down 7.4 per cent year on year - more than can be explained by a 5.9 per cent rise in the exchange rate.