Australia's share market has tumbled to its lowest level since May after jittery investors sparked a plunge on Wall Street.

The S&P/ASX200 had fallen by 103.5 points by midday, down 1.21 per cent, to 8,449.2, as the broader All Ordinaries lost 113.9 points, or 1.29 per cent, to 8,720.1.

The drop followed a grim US session overnight, with solid earnings from the world's biggest company not enough to allay fears about sky-high equity valuations.

"An ugly reversal lower for US equities overnight, erasing the relief rally that followed Nvidia earnings report yesterday morning," IG market analyst Tony Sycamore said.

"The reversal was triggered by several factors: the mixed September jobs report failed to revive hopes of a December Fed rate cut; Nvidia's earnings results failed to quell unea

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