Trading has been halted on the New York Stock Exchange because of a technical issue.
The halt occurred at about 11.30am local time.
The exchange said in a statement that it was experiencing a "technical issue" that it was working to resolve as quickly as possible.
Before trading was halted, US indexes were lower as investors worried about China's ability to stem a stock market slide.
European markets were broadly higher as talks continue on Greece's debt woes.
Trading continued on Nasdaq and other exchanges.
The exchange said on its official Twitter feed that the issue was internal and not related to a breach of its systems.