SINGAPORE (Reuters) -Asian stocks extended an overnight selloff on Wall Street in early trading on Wednesday as investor concerns about stretched valuations sapped confidence.

MSCI's broadest index of Asia-Pacific shares outside Japan was down 0.8%, led by declines in South Korean shares with a loss of 4.1%. U.S. e-mini futures moved 0.4% lower after a 1.2% drop for the S&P 500 overnight.

"It's a sea of red across broad markets," said Chris Weston, head of research at Pepperstone Group in Melbourne. "There aren't many reasons to buy here, and until we move closer to Nvidia's earnings on 19 November, the market lacks a short-term catalyst."

Stocks are retreating from record highs on fears equity markets may have become overstretched after the CEOs of Wall Street heavyweights Morgan Stanley and Goldman Sachs questioned whether sky-high valuations can be sustained.

Last month, banking giant JPMorgan Chase's CEO Jamie Dimon had warned of a heightened risk of a significant correction in the U.S. stock market within the next six months to two years.

The warnings come as a surge in enthusiasm for generative AI has swept across stock markets worldwide this year, drawing comparisons to the dot-com bubble.

Japan's Nikkei stock index slid 2.5%, with SoftBank Group shares plunging 10%.

The U.S. dollar dropped 0.2% against the yen to 153.41 after the release of minutes from the Bank of Japan's September policy meeting,

The dollar index, which tracks the greenback against a basket of currencies of other major trading partners, briefly touched a five-month high of 100.25.

The yield on benchmark 10-year Treasury notes edged lower to 4.0697% compared with its U.S. close of 4.091% on Tuesday.

Bitcoin fell below $100,000 for the first time since June, but rebounded afterwards and was last up 0.2% at $100,499.70. Gold attempted to recover after three consecutive days of losses, and was trading 0.1% higher at $3,936.48 per ounce. [GOL/]

The European single currency was little changed in early trading at $1.1484 after hitting a three-month low following five straight days of declines.

Brent crude was last unchanged at $64.44 per barrel.