New Zealand's export commodity prices made their biggest monthly rise in 22 years in September, rising 6.8 per cent in world price terms from August, the ANZ Commodity Price Index shows.

However, also two thirds of this gain was wiped by the rise in the New Zealand dollar, with local currency prices rising 2.4 per cent.

A rising New Zealand dollar since March has generally wiped out gains in commodity prices as global demand for commodities strengthened following the worst of the credit crisis.

"While the New Zealand dollar strengthened significantly last month (which dampens returns locally), the overall lift in commodity prices was far stronger than the rise in the value of the kiwi dollar," ANZ economist Steve Edwards said.

The 2.4 per cent rise in New Zealand dollar terms was off a cyclical low in August, Edwards said.

"This latest improvement (in world price terms) comes on top of some steady rises made over the last few months. The overall gain since the recent low recorded in February is a cumulative 20 per cent," Edwards said.

"The previous record highs recorded in 2008 were underpinned by a spike in world dairy prices. A similar pattern has lifted the index over the past seven months.

Dairy prices lifted 17 per cent last month, with a cumulative gain of 33 per cent in global dairy prices since February," he said.

"Price rises were noted for seven other commodities. The price of skins recovered 8.3 per cent, sawn timber lifted 7.2 per cent and wool prices rose 5.3 per cent. Smaller increases were noted for wood pulp (3.1 per cent), lamb (2.3 per cent), beef (2.2 per cent) and kiwifruit (0.4 per cent)."

"Declines were measured in the price of apples (-5.7 per cent), aluminium (-4.0 per cent) and logs (-3.0 per cent)."