The Australian stock market closed flat amid mixed company earnings reports and concern over BHP Billiton's credit rating in light of its takeover offer for Canada's PotashCorp. The benchmark S&P/ASX200 index was up 4.1 points, or 0.09 per cent, at 4,479 points, while the broader All Ordinaries index had added 5.7 points, or 0.13 per cent, to 4,509.6 points.

On the Sydney Futures Exchange, the September share price index contract was seven points lower at 4,457 points, on volume of 24,044 contracts. Standard & Poor's has put BHP Billiton's long term issuer credit ratings on watch and says it's likely to lower the mining giant's rating by one notch to 'A' if its $42.89 billion tilt for PotashCorp succeeds.

Fellow international ratings agency Moody's warned the same on Wednesday. BHP Billiton shares were down 12 cents at $38.30, while Rio Tinto shares were 27 cents weaker at $73.18 following weaker metals trading in London overnight.

The big four banks were mostly lower. Commonwealth Bank was down 29 cents at $50.36, ANZ had eased 14 cents to $22.40, Westpac had fallen 11 cents to $22.94, but National Australia Bank bucked the trend, gaining nine cents to $24.40. Brambles shares were up 21 cents, or 3.96 per cent, at $5.51 after reaching a high of $5.71 in intraday trade.

Shares in Wesfarmers were up 15 cents at $31.95. In other news on Thursday, shares in AMP slipped 4.32 per cent to $5.09 the lowest in more than a year after the wealth manager increased first half profit by 17 per cent and expressed caution about the global economic outlook and ongoing market volatility.

The spot price of gold in Sydney was $1,229.20 per fine ounce, up $5.79 on Wednesday's closing price of $1,223.41. Among gold mining stocks, Newcrest was 35 cents higher at $35.36 and its takeover target Lihir Gold was up two cents at $4.38. The top traded stock by volume was Telstra with 157.4 million shares changing hands worth $472.4 million. Telstra shares were up six cents, or 2.03 per cent, at $3.02. Preliminary national turnover reached 2.14 billion shares, worth $6.06 billion, with 530 stocks up, 462 down and 398 unchanged.

The Australian dollar sank in Asia trade Thursday as renewed economic concerns in Europe weighed on risk currencies globally. Australian bonds edged higher once again, continuing an upward trend that has now lasted more than a week.

Much of the Australian dollar's slide occurred overnight when news reports hinted that Greece's response to its debt crisis may push unemployment in that country exponentially higher.

From there, Australian dollar bulls were kept on the sidelines by an ongoing federal electoral campaign. With Australians set to go to the polls on Saturday, a lack of clarity on the outcome has created another layer of uncertainty for those looking to gauge the state of the Australian economy.

The Australian dollar was quoted at $0.8976, down from $0.9020 late Wednesday. Against the Japanese yen, the Australian dollar was at 77.115, from 77.12.