Stocks fell and oil and commodity prices tumbled as traders struggled to measure the effects of a disaster in one of the world's most important and inter-connected markets.

"Anyone who tells you that they have a handle on the economic consequences of this event is wrong," said Carl Weinberg, a top economist with High Frequency Economics, reflecting the market's nervousness.

"There is no way to assess even the direct damage to Japan's economy or to the global economy. This is a sad day for Japan, and economic aftershocks could affect the whole world's economy."

With Japan tied into almost every sector of the global economy, the US stock market's early session sell-off was broad based.

Banks, oil companies, shipping firms all lost value in early trade. Only the US tech and airline sectors seemed unaffected.

The Dow Jones Industrial Average lost 17.75 (0.15 percent) at 11,966.86 minutes after the opening bell, while the broader S&P 500 was down 0.76 points (0.06 percent) to 1,294.35.

Meanwhile the tech-focused Nasdaq Composite rose 1.02 points (0.04 percent) to 2,702.04.

Toyota's US shares sank 2.7 percent. Merck, Caterpillar, Chevron and Bank of America all posted losses.

Airline stocks rose on the prospect of lower oil prices.

Crude prices sank on the prospect of lower consumption in Japan, the world's third largest oil importer and consumer.

The disaster came a day after a massive Wall Street sell-off, caused by a wider-than-expected US trade deficit, a rare trade shortfall in China, new sovereign downgrades in Europe and turmoil in Saudi Arabia and Libya.

"The market's focus has completely changed," said David Campione of Briefing.com.

"Beyond the terrible human toll, the economic impact will be significant and could increase as there are tsunami warnings for Hawaii and the (US) West Coast."