Markit

The Labor Department said Friday that the jobless rate fell to 5.1 percent — a level consistent with a normal economy and the lowest since April 2008 — from 5.3 percent in July.

Though hiring in August was the slowest in five months, the government revised up job growth for June and July by a combined 44,000. From June through August, the economy added a robust 221,000 jobs a month, up from an average of 189,000 from March through May. Three years of solid hiring have put nearly 8 million more Americans to work.

Bank shares suffered most, hitting or nearing the daily trading limit of a 30 percent loss.

"There's a sense of panic," said Evangelos Sioutis, financial analyst and head of equities at Guardian Trust. He noted some traders are selling stock merely to raise cash because there is so little liquidity in the Greek economy.

"There are no buyers," he said. "The outlook is not clear."