Australian shares fall again, dropping to 3-week low

It was down 64.4 points, or 0.89 per cent, to a three-week intraday low of 7,149.4, while the broader All Ordinaries had dropped 68 points, or 0.92 per cent, to 7,324.9.

With the United States perhaps just a week away from hitting its $US31.4 trillion debt ceiling and being unable to pay its bills, Fitch Ratings placed its sterling AAA rating on "rating watch negative".

"The brinkmanship over the debt ceiling, failure of the US authorities to meaningfully tackle medium-term fiscal challenges that will lead to rising budget deficits and a growing debt burden signal downside risks to US creditworthiness," Fitch said.

Negotiators for President Joe Biden and US House Speaker Kevin McCarthy said they held a productive four-hour meeting at the White House, but a number of issues remained unresolved.

Tech stocks were the only sector in the green in midday, possibly boosted by a surge in Nvidia shares in after-hour trading on the Nasdaq.

Nvidia shares rose by as much as 26 per cent after the company said it was boosting supply to meet surging demand for its artificial intelligence chips.

The ASX tech sector was up 1.4 per cent at midday, with Altium up 1.8 per cent, Weebit Nano climbing 3.1 per cent and Brainchip adding 1.9 per cent.

The heavyweight mining sector was the biggest loser, down 1.3 per cent, with BHP falling 1.1 per cent to $42.35, Fortescue Metals down 2.3 per cent and Rio Tinto dropping 0.9 per cent.

The Big Four banks had all lost ground, with CBA, ANZ and NAB all down around 1.2 per cent and Westpac falling 0.9 per cent.

Adbri had jumped 13.1 per cent to a nearly three-month high of $1.81 as the cement maker held its annual general meeting. 

Treasury Wine Estate had dropped 5.8 per cent to a nine-month low of $12.025 after the winemaker said its commercial wines - brands priced under $10 - were struggling and it was reviewing that portfolio.

The Australian dollar was buying 65.32 US cents, from 65.72 US cents at Tuesday's ASX close.