New Zealand's annual food prices were 4.5 per cent higher in December 2021, the biggest annual increase since September 2011 when the annual food prices increased 4.7 per cent, the statistics department Stats NZ said on Thursday.

The main contributor to this increase was higher prices for tomatoes, it said, adding tomatoes nearly doubled in price between December 2020 and December 2021, increasing 99 per cent, reports Xinhua news agency.

The weighted average price of 1 kg of tomatoes increased from NZ$3.33 in December 2020 to NZ$6.61 in December 2021, consumer prices manager Katrina Dewbery said in a statement.

Higher prices for tomatoes were partly offset by cheaper prices for kiwi fruit, kumara, and avocados, Dewbery said.

At a more aggregated level, grocery foods had the biggest impact on the annual food prices movement, increasing 4.5 per cent.

Within this, yoghurt, standard two-litre milk, and fresh eggs were the main contributors, she said.

Overall food prices rose 0.6 per cent last month. This shows that food prices increased by more than they usually do in December, Dewbery said.