The Australian bourse held its ground in the black by Thursday noon, although stocks have trimmed some opening gains as profit-taking set in.

At midday, the benchmark S&P/ASX200 index edged up 34.2 points or 0.8 per cent at 4529.9. The broader All Ordinaries index, meanwhile, had improved 33.7 points or 0.7 per cent to 4560.5.

The S&P/ASX200 is 4 per cent stronger so far this week at a three-week high following Wednesday's data that showed the economy expanded 1.2 per cent in the June quarter - the fastest in three years.

"I suspect we might see a bit of selling into strength today. People are viewing September as a particularly nervous point for markets," according to Angus Gluskie, portfolio manager at White Funds Management.

He said market players possibly reluctant ahead of significant US job data scheduled for release on Friday and nervous investors were aggressive, looking for reasons for renewed selling.

"You're getting a lot of quick knee-jerk reactions in both directions, up and down. These disparate pieces of economic data are being reacted to but the information is by no means clear. We've had some very contradictory information," he said.

But the upbeat mood remained amid strong gains in minerals and financial companies.

Miners continued to edge up after Chinese manufacturing rebounded modestly in August following slowing for several months, and copper prices hit a four-month high.

The large miners and major retail banks were all about 1 per cent higher, outperforming the broader market.

BHP Billiton improved 36 cents or 1 per cent at $38.27. Rio Tinto had climbed to $73.43 after adding $1.19 or 1.7 per cent.

Leighton Holdings was the best-performing stock on the S&P/ASX50. It gained 2.8 per cent or 87 cents at $32.41.

Shortly after midday AEST, there were 21 stocks gaining for every 10 that had slumped.

The stock market started about 1.2 per cent stronger, taking its cues from a solid, positive finish in Wall Street.