"The regulatory authorities are evaluating this closely with a concern to protecting investors and preventing this from happening again," Obama said.

"They will make findings of their review public along with recommendations."

Analysts have suggested that human error was behind the crash - that a trader typed the wrong instructions into a computer.

"The most likely explanation seems to be the 'fat fingers' explanation, that someone entered 'billion' when they meant to enter 'million,'" Al Jazeera's John Terrett said.

Volatile trading

Other markets around the world had bumpy rides on Friday. The European debt crisis is blamed for drops on bourses in Japan, South Korea, Australia and the UK.

China's benchmark Shanghai index tumbled 2.4 per cent in early trade, before rallying to end the day 1.9 per cent down. Shares in Taiwan, Singapore and New Zealand also fell sharply.

In the United States, the Dow Jones Industrial Average dropped by more than 300 points in early trading; it recovered some of its ground shortly before noon, and closed down 140 points, a 1.3 per cent drop.