World dairy prices have fallen nearly 1% in Fonterra's overnight auction, the first fall since mid-July.
The Global Trade Weighted Dairy Index shows a drop of 0.9%. The price had risen in the previous four auctions.
The average winning price was $US3,285 a tonne.
Prices for whole milk powder, one of the largest products by volume sold, rose 2.8% while skim milk powder fell 0.9%.
Rennet casein, anhydrous milk fat, cheddar and lactose all recorded big falls.
BNZ economist Doug Steel says the index has taken a breather after picking up from expected offshore supply shortages in the coming months.
He says world economic indicators are looking patchy and there is a lot of concern around Europe which makes it difficult to determine what is going to happen next.
Mr Steel says there is likely to be some choppiness in the short term.