In seasonally adjusted terms exports were down 5.9 per cent last month compared with June. This was despite higher dairy and meat exports - up 13.2 per cent and 3.5 per cent respectively - and a 7.3 per cent increase in exports of mechanical machinery and equipment, which followed a 33 per cent rise in June.
ASB economist Christina Leung said the improvement in manufactured exports was encouraging given the emerging headwinds manufacturers faced, particularly slowing growth in Australia and a higher exchange rate with the Australian dollar.
The main declines in seasonally adjusted exports last month were in crude oil and aluminium, after unusually strong volumes exported in June.
Westpac economist Michael Gordon said: "We expect volatility in the trade figures to continue for the next few months as a number of large movements - think drought and large swings in currencies - throw the balance around."
Dairy prices in recent months had been puzzlingly soft, he said.
The Canterbury rebuild and its associated demand for imports would increasingly dominate the trade balance heading into 2014, Gordon said.
"We expect trade deficits to persist from that point."