Both the New York Stock Exchange (Nyse) and American Stock Exchange (Amex) were forced to suspend trading four minutes early on Wednesday due to a "network problem".
Trading was halted four minutes before the exchanges' usual 4pm closing, one of the busiest times of the day.
A spokesperson from Amex told Reuters reporters that the exchange had a network problem but will be be back trading normally on Thursday.
Citing a trading floor source, Reuters says the problem originated at the Securities Industry Automation Corporation (SIAC), a technology centre co-owned by Nyse and Amex which runs the computer systems and communications networks that power the two exchanges and disseminates market data.
The Nyse issued a brief statement following the incident saying trade stopped at 3:56 pm (ET) due to a "communication problem" and that trading did not resume and all crossing sessions were cancelled. Nyse also cancelled its after hours trading and said trading will open Thursday morning.