Australian dollar set to seal best year since 2010, NZ$ lags

The Australian dollar was taking in the view at $0.7802, having touched a 10-week top of $0.7810 overnight. That left the commodity currency with gains of more than 8 percent for the year, its best showing since 2010.

That performance would be a surprise to many given that a global Reuters poll of analysts at the start of the year found the Aussie would 2017 at 72 U.S. cents.

Surprising resilience in Chinese demand for commodities, including iron ore - Australia's biggest export earner - has certainly helped. The mineral currently fetches more than $70 a tonne after having been down around $50 a few months ago.

Industrial bellwether copper was also on a tear, hitting a four-year peak to be up 30 percent for 2017.

Yet some wonder how long the Aussie could defy gravity given official U.S. interest rates were almost certain to move above Australia's next year.

The premium offered by Australian two-year bonds over their U.S. counterpart is already down to almost nothing and set to turn negative for the first time since 2000.

"Risk is rates differentials will move further against the AUD at the front end of the curve at least," said Ray Attrill, NAB's head of forex strategy.

NAB expects official U.S. rates to reach 2 percent by mid-2018, fully 50 basis points above the Reserve Bank of Australia's cash rate.

"Even on current differentials AUD is seen moving into a lower $0.70-$0.75 trading band in the first half, with downside risks depending on broader U.S. dollar performance, risk sentiment and commodity prices," added Attrill.

Across the Tasman Sea the New Zealand dollar edged up to $0.7098 having also reached a 10-week peak overnight.

The kiwi was 2.3 percent firmer for the year, a relatively solid performance given it had to weather a bout of political uncertainty when the country's long-serving conservative government lost power.

Australian government bond futures inched ahead for a third session. The three-year bond contract added 3 ticks to 97.835, while the 10-year contract rose 1 tick to 97.3150.