The Australian dollar has been hit by another sudden sell-off, falling more than half a cent this afternoon as investors flee the currency.

The dollar fell as low as 97.32 US cents, a level not seen since early June 2012, and down from 99.12 US cents about midday on Thursday.

Sell in May ... the dollar has slumped 5 per cent this month. Credit:Louie Douvis

It's been a particularly volatile 24 hours for the currency, which was fetching 99.12 US cents as late as yesterday midday. During the offshore session it plunged to 97.9 US cents but quickly recovered, touching a high of 98.79 shortly after midnight. By morning it was buying 98.22 US cents, before the latest sell-off was triggered.

But the currency is not only falling against the greenback - versus the euro it's dropped to 75.80 euro cents, its lowest since December 2011. And even against the yen it's under pressure, slipping back below 100 yen.