Hong Kong - Asian markets suffered a sell-off on Wednesday after a US Federal Reserve head said the central bank's huge stimulus plan unveiled this month might not boost the economy as much as hoped.
Eurozone debt fears were also fuelled after a European Central Bank (ECB) official said it could not restructure Greece's debt with the regional lender, while tensions between China and Japan continued to weigh on markets.
Tokyo fell 1.71% by the break, Hong Kong was down 0.88%, Sydney shed 0.40%, Shanghai lost 0.32% and Seoul slipped 0.61%.
The global excitement stoked over the past month following stimulus announcements in the US, Japan and Europe was given a jolt after the head of the Fed's Philadelphia branch questioned the impact of the US bank's move.
Charles Plosser said he was doubtful the unlimited bond-buying programme unleashed by the Fed would charge up the US economy, and warned that the Fed could lose credibility because of it.
IG Markets said in a report: "Many traders feel central bank stimulus is merely a sticking plaster for a broken leg, and that much more needs to be done to send the global economy safely on the road to recovery."
His comments reversed an early Wall Street rally that had been fuelled by upbeat data on consumer confidence and house prices.
By the end of trade the Dow fell 0.75%, the S&P 500 lost 1.05% and the Nasdaq shed 1.36%.
In Europe, worries over Greece were back in focus as ECB executive board member Joerg Asmussen dismissed an idea raised by Athens that Greek bonds at the bank could be rolled over to bridge a fresh financing gap in the country.
He told Germany's Die Welt daily such a move would be "forbidden monetary financing".
His comments came after Greek deputy finance minister Christos Staikouras last week told parliament the maturity of Athens' bonds owned by the ECB and worth around 28 billion euros could be extended by mutual agreement.
Greece is struggling to apply a fiscal overhaul mandated by the ECB, European Union and International Monetary Fund in return for a new tranche of bailout cash.
On currency markets the euro bought $1.2905 and ¥100.40 in early Asian trade on Wednesday against $1.2902 and ¥100.36 in New York late on Tuesday.
The dollar was at ¥77.78 against ¥77.79.
In Tokyo and Shanghai, shares were also under pressure because of the ongoing diplomatic spat between the two countries over a group of islands in the East China Sea.
The row, which has seen violent protests across China, has hit China-linked Japanese firms. And on Wednesday car giants Toyota and Nissan said they would cut production in the country because demand for their cars had tumbled.
By the break in Tokyo Toyota Motor had dropped 1.72% and Nissan Motor lost 2.05%.
"In the foreground there seems to be geopolitical risk between Tokyo and Beijing," Matthew Sherwood, head of investment market research at Perpetual Investments in Sydney, told Dow Jones Newswires.
"People are still quite worried about Japan's export-based economy."
Oil prices weakened, with New York's main contract, light sweet crude for delivery in November sinking 25 cents to $91.12 a barrel and Brent North sea crude for November delivery shed 45 cents to $110.00.
Gold was at $1 763.60 at 03:00 GMT compared with $1 764.30 on Tuesday.
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