To watch a video of the market drama, click on the video at left.

But Citigroup said "At this point, we have no evidence that Citi was involved in any erroneous transaction" and the head of the NYSE said "I don't think you are looking for one bank that traded the wrong number of shares."

Other trading anomalies were also emerging: Accenture , a $40 stock, at one point dropped to one cent. ONE CENT. And 3M shares had a wild swing in afternoon trading, falling to around $68, before popping to $90 and finally settling at $84.24.

All this fogginess about botched trades came as the market was already on edge about Greece and the European debt crisis.

Just before the panic started, which was around 2:30pm ET, Mohamed El-Erian said on CNBC that the Greek crisis is about to spread.

"We've seen a crisis start in a country—Greece—become regional, impact the whole of the Euro zone and is on the verge of truly going global," said El-Erian, CEO of the world's biggest bond fund.

Rochdale analyst Dick Bove said the riots in Greece, which escalated after the Greek austerity bill was passed, are also a telling sign.

"There is simply a growing recognition that Greece has got to default, said Rochdale banking analyst Dick Bove. "The riots in the streets showed the decision to repay the debt was not going to be made by the people in Germany, France and Switzerland, it's going to be made by people in Greece and they're not going to repay it," he said. "Anyone seeing the riots is going to recognize that this government is going to be thrown out and anything replacing this government is going to be far more leftist leaning and they're going to repudiate."

Financials were pummeled, with Bank of America down more than 7 percent and JPMorgan off more than 4 percent. US-traded shares of Barclays were off 11 percent.

Financials had actually started the day under pressure after the U.S. Senate approved an amendment to the financial-reform bill that would end "too big to fail." The selling just accelerated as the riot news and European-lending rumors spread.

Earlier, the European Central Bank opted to keep interest rates unchanged, which came as a disappointment to the market as many had hoped that the central bank would take some action to stem the current crisis. The market also didn't like that ECB president Jean-Claude Trichet used the "u" word — uncertainty.

"We expect the euro-area economy to expand at a moderate pace in 2010, but growth patterns could be uneven in an environment of high uncertainty," Trichet said.

While debt worries spread to what seems like a new European country each day — Greece, Spain, Portugal — Standard & Poor's reiterated that their outlook for Italy is stable.

The dollar jumped to a 14-month high against the euro after the ECB failed to offer any additional measures to ease the Greek debt crisis. Oil fellto $77.11a barrel and gold soaredto $1,201 an ounce as investors piled into the metal as a safe haven from the market madness.

One trader noted that today just may be the day gold became a currency.

Elsewhere in the financial sector, Freddie Mac will ask for $10.6 billion more in federal aid after posting a nearly $8 billion loss in its latest quarter.