The New York Stock Exchange unexpectedly shut down trading in all of its listed stocks late Wednesday morning.

According to the New York Times, the exchange did not immediately give an explanation for what caused the shutdown. Later, on Twitter, the exchange said: “The issue we are experiencing is an internal technical issue and is not the result of a cyberbreach.”

The New York Stock Exchange has had technical difficulties in the past, but the scale of the problem on Wednesday has little precedent. Stocks listed on the New York Stock Exchange continued trading on other exchanges, like Nasdaq.