The rapid unravelling of the US dollar has unleashed a rally across currencies and commodities as traders frantically position for the Federal Reserve to kick off its easing cycle next month.

The US dollar index slid 0.8 per cent to a low of 100.60 points, its weakest level since July last year, after Fed chairman Jerome Powell said at the Jackson Hole symposium that the time has come to cut rates. The greenback held on to those losses on Monday and is now down more than 2 per cent in August.