In Athens, the ASE index dropped 3.6 per cent to its lowest in more than two decades.
In afternoon trading, the Dow Jones Industrial Average sank 1 per cent, the Standard & Poor's 500 Index dropped 1.01 per cent and the Nasdaq Composite Index fell 1.04 per cent.
Investors are fleeing to the perceived safety of both US Treasuries and German bunds.
A US$32 billion auction of three-year US notes drew a yield of 0.362 per cent, compared with a forecast of 0.365 per cent in a Bloomberg survey of seven of the Fed's primary dealers. The yield on the benchmark 10-year note declined to 1.83 per cent.
Meanwhile, corporate earnings continue to lack the lustre of the season's initial couple of weeks. While first-quarter results are still ahead of expectations for about two-thirds of the US companies who have reported so far, that ratio is not quite enough to instill confidence needed to push Wall Street higher.
Today, shares of McDonalds dropped more than 2 per cent on disappointing sales, while those of Fossil plunged 37 per cent on a downgraded full-year outlook because of weakness in Europe.
"For the past six weeks or so, what's been really holding us is the earnings. Now that big earnings are out, the focus is back to Europe, at least in the short-term," Randy Warren, chief investment officer at Warren Financial Service & Associates in Exton, Pennsylvania, told Reuters.
"A break below the recent trading range suggests that if we get a pullback, we could go below our 200-day moving average of about 1,275 which is down about 8-10 per cent from here," Warren said.
The S&P 500 was last trading at 1,355.68, below the 1360-mark, considered to be a key technical point.