BNZ head of research Stephen Toplis said no-one expected the biggest December trade surplus as a share of exports since 1991, but that was what Statistics New Zealand figures showed yesterday.
The annual trade deficit narrowed to $1.21 billion from $1.39 billion in the 12 months to November.
''We don't think it will be enough to stop the deterioration in the current account, but at least it will lessen the slippage.''
BNZ was still forecasting the current account deficit to go above 5% of gross domestic product (GDP) in the December quarter from the 4.7% recorded in September.
The lower imports were ''strictly positive'' from a growth accounting point of view. But that need not be the case in the bigger picture, if the lower imports were reflecting something of a slow-down in domestic demand, Mr Toplis said.
''Not that one month's data would convince us either way, but looking through the details, we do not think that the import slump indicates a downturnin domestic demand.''
Some of the fall in imports reflected large one-off imports from a year ago, like helicopters. December exports were stronger than market expectations, falling by 5.1% rather than the 7.1% fall anticipated, Mr Toplis said.
''Again, we wouldn't read too much into one month but it does add a bit more support to income in the fourth quarter relative to previous expectations,'' he said.
ASB economist Jane Turner said the fall in exports during the December quarter was led by a fall in dairy exports.
That was due to falls recorded in August through to October as exports corrected to more normal levels, following a strong end to the previous season.
Exports had since picked up in November and December on a promising start to the season and pointed to a recovery in exports in the March 2013 quarter.
However, if the dry conditions in the North Island continued to persist, poor grass-growing conditions and high feed costs could limit this season's production performance, she said.
Manufacturing exports also weakened in the fourth quarter, probably reflecting slower demand from Australia and the United States.
''We do expect to see some recovery in demand from these regions over 2013.''
The Reserve Bank of Australia rate cuts should stimulate demand thereand reduced fiscal uncertainty in the United States should see its orders for capital goods recover, Ms Turner said.
Green Party co-leader Russel Norman said the falling manufactured exports provided further evidence of a growing crisis in manufacturing.
Dr Norman said Economic Development Minister Steven Joyce denied there was a problem but the evidence showed the manufacturing sector was in trouble.
''On Planet Joyce, there's no crisis in manufacturing, despite the ongoing decline in manufactured exports and the loss of 40,000 jobs in the sector since 2008,'' Dr Norman said.
Mr Joyce dismissed claims the country faced a manufacturing crisis, saying some companies were prospering with a high dollar.
Yesterday, he attempted to water down fears raised by business leaders at the Opposition's parliamentary inquiry into manufacturing.
Opposition MPs were told more leading export companies were on the verge of moving overseas, due to the high dollar, and they challenged the Government to do more to control the exchange rate.
''The reality is, for some companies, it is a challenging time,'' Mr Joyce told Radio New Zealand.
''Other companies are doing very well and I could make you a large list, a long list of New Zealand exporters that are doing very well in the current environment. But that's the nature of it.''
Mr Joyce said businesses exposed to different parts of the exchange rate faced different challenges if the dollar was high or low.
It would be ''putting false hope into peoples' minds'' to suggest the Government could have ''a massive influence on the US dollar''.
He expected a ''better year'' for the United States this year.
Balance: $486m surplus (forecast $105m deficit)
Exports: $4.07b (forecast $3.98b)
Imports: $3.58b (forecast $4.13b)
Annual balance: -$1.21b (previous -$1.39b)