For the second month in a row ANZ's export commodity price index has risen and September's 3.5 per cent increase is its strongest monthly gain for a year and a half.

It is too early yet to book the cathedral for a performance of the Hallelujah Chorus, ANZ economist Steve Edwards said. "But it is encouraging."

Ten of the 17 commodities in the index rose, but the gains were heavily concentrated in dairy products, which make up 43 per cent of it. Excluding them the rise would have been 0.5 per cent.

The index is still 16.9 per cent off its peak of April last year in world price terms.


Most of last month's gain survives the exchange rate.

In New Zealand dollar terms the ANZ index rose 3 per cent, though it remains 24 per cent off its peak of 18 months ago.

"It's a welcome break from nine months of almost uninterrupted declines," Edwards said.

Both skim milk powder and aluminium prices jumped 11 per cent in September.

Butter and whole milk powder rose 8 per cent, wool and apples 6 per cent, cheese 5 per cent, venison 2 per cent, and logs and beef 0.5 per cent.

Prices fell for pelts by 10 per cent, casein and kiwifruit were down 2 per cent and lamb dropped 1 per cent.

The drop in lamb prices had been as sharp as the rise was a couple of years ago, Edwards said.

"Offsetting that, beef and venison have picked up a little bit."

The Treasury, reflecting on Monday on the past month's crop of economic indicators, pointed to signs that export commodity prices might have found a floor as a potential boost to the economy in the near term.

"Admittedly, prices remain some way below their peaks reached last year, and the recent gains in the New Zealand dollar have taken the edge off," it said.

Nonetheless, Fonterra's GlobalDairyTrade index of dairy prices had climbed by over 20 per cent over the past four fortnightly auctions (before the event due overnight) reflecting, at least in part, concerns about the impact of drought in the United States on the supply of grains, it said.

"Beyond the anticipated short-term drought-induced rise in global beef supply and associated fall in prices, the reduced size of the US cattle herd will lead to a further tightening in beef supply and higher prices."