At noon AEST on Thursday, the benchmark S&P/ASX200 index was down 31 points, or 0.36 per cent, to 8,566.7, while the broader All Ordinaries had slipped 27.9 points or 0.32 per cent, to 8,799.7.
Just three of the ASX's 11 sectors were in the green at midday - health care, energy and materials.
The latter was the biggest gainer, rising 2.1 per cent after China vowed to crack down on "disorderly low-price competition" in the steel industry and phase out some industrial capacity.
"The move shows China's leaders are trying to tackle deflationary pressures weighing on the economy," ANZ researchers Brian Martin and Daniel Hynes wrote in a note.
"The plans should also bring some relief to the steel industry, which has been weighed down by overcapacity."
BHP was on track for its best day since April 10, rising 4.3 per cent to $38.81.
Rio Tinto had advanced 1.5 per cent, Fortescue had climbed 0.9 per cent and Mineral Resources was up 5.7 per cent.
In the energy sector, coalminers were ascendant, with Whitehaven gaining 9.4 per cent and New Hope advancing 6.1 per cent.
But uranium plays were losing ground, with Boss Energy down 7.4 per cent, Bannerman sliding 5.8 per cent and Paladin subtracting 4.7 per cent.
The big four banks were also mostly lower, with CBA declining 1.6 per cent, Westpac subtracting 1.0 per cent and NAB down 1.3 per cent.
ANZ was the outlier, edging 0.2 per cent higher.
In the consumer sector, Kmart owner Wesfarmers had declined 2.3 per cent, JB Hi Fi had dropped 5.6 per cent and Aristocrat Leisure had slipped 1.8 per cent.
In health care, Pro Medicus had advanced 6.2 per cent after the medical imaging giant signed a $170 million, 10-year contract to provide services to a chain of 14 hospitals in Colorado, Wyoming and Nebraska.
The Australian dollar was buying 65.69 US cents, from 65.70 US cents at midday on Wednesday.
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