Food prices have risen at their fastest annual rate in 13 years.

Stats NZ data showed the food price index rose 1.1 percent in August on the month before, to be 8.3 percent higher than a year ago - the biggest annual increase since July 2009.

The monthly increase was driven by a 4.1 percent rise in fresh fruit and vegetables, with bad weather affecting production in some key growing areas.

"Vegetables had the largest impact on this monthly rise, influenced by higher prices for tomatoes, capsicums, and cabbage," Stats NZ consumer prices manager Katrina Dewbery said.

Grocery prices were the second biggest contributor to the monthly increase, rising 1.0 percent, on the back of a 6.7 percent rise in prices for eggs, yoghurt, up 4.7 percent, and chocolate biscuits, up 7.1 percent.

On an annual basis, an 8.7 percent rise in grocery food prices was the main driver of the increase, particularly in eggs and some dairy products.

Fruit and vegetable prices increased 15 percent, but have a lower weighting in the overall food price index (FPI).

All the other sub-groups making up the FPI rose over the year:

restaurant meals and ready-to-eat food prices by 6.5 percent; meat, poultry, and fish prices by 7.6 percent; non-alcoholic beverage prices by 4.1 percent.

Food prices make up about 19 percent of the overall consumer price index, which increased 7.3 percent in the year ended June.

Main image: The annual increase in grocery prices was driven by the rising costs of eggs, yoghurt, and cheddar cheese.