The New York Stock Exchange (NYSE) has suspended trading in all securities on the NYSE and NYSE MKT for an unspecified technical issue, the exchange announced on Wednesday.

The exchange temporarily suspended trading in all symbols, and cancelled all open orders, at 11:51 ET today.

“We’re experiencing a technical issue that we’re working to resolve as quickly as possible,” it said in a statement on Twitter, adding, “We’re doing our utmost to produce a swift resolution and will be providing further updates as soon as we can.”

The NYSE stressed that the issue disrupting trading is “an internal technical issue and is not the result of a cyber breach.” The exchange chose to suspend trading on its markets to avoid problems stemming from the issue, and to allow its listed securities to continue trading on other venues, it said.

The NYSE Arca and Amex/Arca Options markets are not affected by the shutdown, nor is Nasdaq trading in NYSE listings.

Although it still has yet to explain the reason for today’s trading outage, the NYSE is now planning to resume trading shortly after 15:00 ET today. It will begin accepting orders and restart trading in NYSE MKT securities at 15:05 ET, with the main market re-opening at 15:10 ET.

Trading is to resume without a re-opening auction, although it is planning to hold closing auctions as normal.