By the end of the week, however, stocks were regaining lost ground as it became apparent that disruption to supplies of components from Japan might not be as great as had been feared initially.

The worst day of the week was Tuesday, when the tech-oriented Nasdaq dropped 33.64 points, the S&P 500 declined 14.52 points and the Dow plunged 137.74 points. It was the Dow's worst day since the middle of last year, when concerns about a double-dip recession hit the markets. Bellwether tech stocks declined along with blue-chip industrials. Apple, for example, had its third-worst trading day on record Tuesday, dropping US$15.42 to $330.01.

Japan does not buy a large percentage of U.S. products. The country buys about 5 percent of total U.S. exports. However, concerns centered more on component and equipment supplies from Japan as companies reported damaged or shut-down production facilities.

Japan in 2010 made up about 14 percent of worldwide electronic-equipment factory revenue, according to an IHS iSuppli estimate this week. In addition, "Japanese suppliers accounted for more than one fifth of global semiconductor production in 2010. Companies headquartered in Japan generated $63.3 billion in microchip revenue in 2010, representing 20.8 percent of the worldwide market," the said.

Another iSuppli report suggested that component shortages could constrain supplies of Apple's iPad. Five iPad parts are sourced from Japanese suppliers, iSuppli said. The components include NAND flash from Toshiba, dynamic random access memory (DRAM) made by Elpida Memory, an electronic compass from AKM Semiconductor, touchscreen overlay glass from Asahi Glass and the system battery from Apple Japan.