Australian shares had fallen further mid-session after opening only slightly weaker, with all sectors trading in the red.
At 9.25am, the benchmark S&P/ASX200 index was down 37.5 points, or 0.84 per cent, at 4410.5 points, while the broader All Ordinaries index had fallen 36.5 points, or 0.82 per cent, to 4433.4 points.
On the ASX 24, the December share price index futures contract was 32 points lower at 4425 points, on volume of 14,482 contracts.
The Australian stock market was recording far heavier losses than expected, after flat overnight leads from offshore markets.
CMC Markets chief market analyst Ric Spooner said he was not aware of any identifiable reason or news that would suggest such heavy falls other than that the ASX had been outperforming US markets in recent days.
"These things feed on themselves a little bit ... I guess we have a situation where our market has outperformed the US market since the presidential election, we haven't fallen as far," he told AAP.
"Sometimes a bit of nervousness gets around and a little bit of selling gets underway."
Investors had already positioned portfolios according to their assessment of the probability of US politicians compromising on plans for tax hikes and spending cuts and a near term exit of Greece from the euro, he said.
The big four retail banks were all weaker.
ANZ was down 19 cents at $24.26 and National Australia had dropped 24 cents to $23.40, while Westpac had shed 42 cents to $24.93 and CBA had given up 40 cents to $59.
Major resources company BHP Billiton was 23 cents lower at $34.07 and Rio Tinto had fallen 19 cents to $58.45.
In closing trade overnight, the Dow Jones Industrial Average was down two points (0.02 per cent) at 12,817.39.
London's FTSE 100 index of top companies edged down a mere 0.04 per cent to 5767.27 points overnight, while in Frankfurt the DAX 30 ended up just 0.07 per cent to 7168.76 points, and in Paris the CAC 40 slid 0.35 per cent lower to 3411.65 points.