"We're seeing a lot of panic selling," said Peter Lai, investment manager at DBS Vickers in Hong Kong. "People are just liquidating ... Nobody can predict where the bottom is."
Tokyo's Nikkei 225 index, after trading higher in the morning, closed down 6.4 percent to 7,162.90 - the lowest since October 1982. Hong Kong's Hang Seng Index tumbled 12.7 percent to 11,015.84, its lowest close in more than four years.
European markets followed Asia lower, with benchmarks in Britain, Germany and France trading down more than 4 percent or more in early trading.
On Wall Street Friday, the Dow Jones industrial average fell 312.30, or 3.59 percent, to 8,378.95. Early Monday, stock index futures were down, signaled a lower open. Dow futures were down 268 points, or 3.2 percent, at 7,994. S&P futures were down about 4 percent.
The sharp declines Monday came amid another round of government measures to boost markets. In South Korea, the central bank slashed its key interest rate Monday by three-quarters of a percentage point - its biggest cut ever - to prevent Asia's fourth-largest economy from lurching into recession.
Australian and Hong Kong central bankers injected funds into their markets to ensure liquidity. Japan's prime minister urged officials to draw up measures to calm volatile stock markets and to fend off further fallout from the crisis.
In Europe, the International Monetary Fund said Sunday it had reached a tentative agreement to provide Ukraine with $16.5 billion in loans and announced that emergency assistance for Hungary had cleared a key hurdle.
Only South Korea's market managed to eke out gains, perhaps in part because of the big rate cut there. The benchmark Kospi ended 0.8 percent higher at 946.45.
In mainland China, the benchmark index slumped to its lowest level in more than two years as investors reacted to dismal earnings reports. The Shanghai Composite Index lost 6.3 percent, or 116.27 points, to 1,723.35. It is now down about 72 percent from its peak about a year ago.
"The panic spread much faster than we expected. It's as if everyone wants to be the fastest runner, with the best escape," said Feng Yuming, an analyst for Oriental Securities in Shanghai.
In the Philippines, the key index plummeted 12.3 percent to 1,713.83 points, triggering a circuit-breaker that automatically halted trading for 15 minutes. The biggest one-day drop since February 2007 was caused by "big fund players" withdrawing investments to get cash and meet redemptions at home, traders said.
Some analysts say the declines are overdone.
"Our fundamentals were ignored; we followed the U.S.," said Emmanuel Soller, broker at EquitiWorld Securities Inc. in Manila.
"But I believe there was an overreaction by investors."
Tuesday's U.S. Federal Reserve meeting was more cause for caution. The central bank is expected to lower interest rates by at least a half-point to 1 percent, though the rate reduction is already priced into the market and unlikely to calm its restlessness.
In Japan, stocks fell despite a report that the government was considering massive capital injection into struggling banks in a bid to calm jittery financial markets.
"The reported plan by the government hardly cheered investors.
What the market really wants is a package of stimulus measures to boost the Japanese economy," said Kazuki Miyazawa, market analyst at Daiwa Securities SMBC Co. Ltd.
Citing unidentified sources, the Yomiuri newspaper said Monday the government is considering injecting public money worth 10 trillion yen ($108 billion) into struggling banks in a bid to stabilize the financial market hit by sagging stocks and a soaring yen.
Investors in Japan dumped exporters like Toyota Motor Corp. and Sony Corp. as the yen remained strong after hitting a 13-year high of 90.89 yen on Friday as investors unwound so-called yen carry trades. The dollar stood at 92.27 yen compared with 94.24 yen late Friday in New York.
Financial ministers and central bank presidents of the Group of Seven major industrial countries issued a joint statement expressing concern about the recent volatility of the yen.
"We are concerned about the recent excessive volatility in the exchange rate of the yen and its possible adverse implications for economic and financial stability," the G-7 finance officials said in a statement released in Washington, Tokyo and other G-7 capitals.
In oil, crude prices weakened after OPEC's move to cut production in an attempt to halt the declines. Light, sweet crude for December delivery was down $2.80 to $61.36 a barrel in Asian trade. The contract settled at $64.15 a barrel on the New York Mercantile Exchange on Friday.
Oil prices have plunged more than 57 percent from a record $147.27 in mid-July.
