The country has experienced its largest January trade deficit since 2007.
Official figures show a shortfall of $566 million last month, as imports rose more than exports.
The deficit contrasts with last month's $596 million surplus, which was the largest ever for a December month.
Exports rose 9.5 percent to $4.3 billion compared with the same period a year ago, led by a rise in the volumes in milk powder, butter, and cheese.
But economists say the higher dollar, lower commodity prices for dairy and meat, and lower volumes of fruit such as apples and kiwifruit due to the weather all weighed on exports.
Imports jumped 17 percent to $4.9 billion, with increases across a range of commodities including turbo-jets, diesel and ships.
"This indicates the domestic economy has started 2018 in reasonable shape," ANZ Bank Agri Economist Con Williams said.
The annual trade deficit widened to $3.2 billion.