(Editor's note: This story is being updated with new developments.)

The world's most important stock market is closed.

This morning at 8:32 a.m., the New York Stock Exchange halted trading. At 9:28 a.m., the NYSE tweeted that this is due to "an internal technical issue and is not the result of a cyber breach".

Interlisted NYSE stocks can be bought and sold on other exchanges, such as Nasdaq.

Shortly after trading was halted, Twitter was ablaze with reports of outages at the Wall Street Journal and United Airlines.

The trading shutdown on the NYSE came after share prices plunged in Asia. The steepest decline came in Shanghai, where the composite index fell 5.9 percent.

More than 1,300 companies halted trading in Shanghai. Shanghai's index is off 32 percent from its June 12 peak.

In Hong Kong, the index fell 5.84 percent, whereas stocks fell 3.14 percent in Tokyo and 2.01 percent in Sydney.

President Barack Obama has been briefed on the New York Stock Exchange closure and his officials are monitoring the situation.