The US dollar hit its lowest level in five weeks against a basket of major currencies and was on course for its worst week since November, hit by a loss of confidence in the US reflation trade a day after a news conference by US President-elect Donald Trump.

The Australian dollar, as expected, has surged above the US75¢ mark amid the greenback's retreat. At about 2.45am AEDT on Friday, the Aussie was 0.8 per cent higher at US75.02¢; it earlier touched US75.19¢. The overnight low was US74.30¢. The local currency has advanced US3¢, or more than 4 per cent, so far this year.

Also helping the Aussie, gold has risen back above the $US1200 an ounce mark and copper has added more than 2 per cent in London to its highest in a month. Nickel, lead, zinc and aluminium also were higher in late trade on the London Metal Exchange. Iron ore edged 58 US cents higher to $US80.99 a tonne.

In addition, oil extended this week's rally after Saudi Arabia said it has cut output to its lowest in almost two years and it expects the market to tighten within three years. Oil also got a boost from China National Petroleum. Reflecting China's growing fuel consumption, its net crude imports will rise 5.3 per cent to 396 million tonnes in 2017, China National Petroleum Corp said. CNPC said its crude demand will hit a record 594 million tonnes this year.

Speculators had driven the dollar index, which measures the greenback against a basket of six major currencies, to a one-week high on Wednesday in anticipation that Trump's first news conference since his November 8 victory would give more detail on new fiscal spending and tax measures to repatriate US corporate capital held overseas.

Instead, the event was dominated by debate over Russian hacking and unsubstantiated claims that he had been caught in a compromising position in Moscow. The dollar index tumbled to 100.720 on Thursday in New York after touching, its weakest since December 8 after touching 102.950 before the news conference the previous day.

"Mr Trump disappointed in not providing deeper details on his policy platform," said Joe Manimbo, senior market analyst with Western Union Business Solutions in Washington.

The dollar index had gained 4 per cent between Trump's election victory and Wednesday on expectations that his promised policies would boost inflation and encourage the Federal Reserve to raise interest rates. The index is on track to fall 1.3 per cent this week to mark its worst week since that ended November 4.

The dollar weakened as much as 1.4 per cent against the yen to 113.76 yen, its weakest level in five weeks, while the euro hit its highest in five weeks against the dollar of $US1.0684 . Sterling hit a six-day high against the dollar of $US1.2317, rebounding from a three-month low of $US1.2038 touched Wednesday before Trump's news conference.

Even the Mexican peso rebounded against the greenback. The dollar was last down 0.7 per cent against the peso at 21.7075 pesos. The peso broke the 22 peso-per-dollar mark for the first time on Wednesday and hit a record low of 22.0440 pesos after Trump said US auto companies would face a high tax for products made south of the border during the press conference.

Analysts said it was unclear how long the dollar weakness would last.

"For the moment, I would stop short of drawing broader conclusions. I think (Trump) will still implement his policy platform," said Lee Hardman, a currency economist with Japan's MUFG in London.