New Zealand imported much less fuel as international travel dried up, and the lockdown meant less travel within the country too, Allen said.
Car imports also fell sharply after the lockdown when non-essential businesses closed, including car yards.
Imports of petroleum and products fell $2.4b in 2020, following Covid-19 travel restrictions.
Imports of vehicle, parts, and accessories also fell, by $2.1b.
In contrast to the sharp drop in imports, annual exports were relatively unchanged in 2020, up $24 million to $60b in the year to December.
Exports of breathing equipment - respiratory equipment - were up $526m, due to high demand during the Covid-19 pandemic.
Fruit exports rose $525m, driven by higher volumes and prices for kiwifruit.
Aircraft and parts rose $435m, as planes were sent to the United States for storage during the slump in international travel.