Buckle up: Fortescue plunge takes shares on bumpy ride

There were no major data releases overnight - that will come later - with a key Australian second-quarter inflation report due Wednesday, followed by decisions on interest rates by central banks in the US, Japan and the United Kingdom.

US tech goliaths Microsoft, Meta, Apple and Amazon are also reporting earnings this week.

Credit Corp kicked off Australian earnings season on Tuesday, with its shares rising 6.1 per cent after the debt buyer announced its full-year net profit was down 11 per cent to $81.2 million, and forecast a $90 million to $100 million profit for 2024/25.

"The stock has been very weak going into the result. We think investor expectations were already very low," E&P Capital analyst Olivier Coulon wrote in a note.

The ASX's materials sector was the biggest loser at midday, down 1.9 per cent as Fortescue plunged 8.9 per cent to a 20-month low of $18.535 amid media reports a mystery institutional investor had unloaded $1.9 billion worth of shares.

BHP had dropped 1.3 per cent, Rio Tinto had fallen 1.1 per cent and goldminer Northern Star had slipped 1.0 per cent.

Most of the big retail banks were lower, with ANZ down 0.9 per cent, Westpac dropping 0.4 per cent and NAB edging 0.1 per cent lower.

CBA was up marginally, by less than a tenth of a percentage point.

Woolworths was down 0.5 per cent after the group announced that Natalie Davis, its managing director for supermarkets, is leaving to become the chief executive of Ramsay Health Care.

She will replace Craig McNally, who will retire in June 2025 after eight years on the job.

Ramsay shares were down 3 per cent.

In the tech sector, Appen had ripped 31.4 per cent higher to a two-month high of 56.5c after the AI dataset company announced its revenue growth in the June quarter had largely offset the loss of a major contract with Google.

The Australian dollar was buying 65.46 US cents, from 65.56 US cents at Monday's ASX close.