NASDAQ index flatlines after the exchange halts trading Thursday afternoon. Nasdaq Trading in stocks and options on the NASDAQ has been halted as of shortly after noon.

Now, the exchange is saying trading in stocks will resume at 3:25 PM, while options trading will be back online at 3:35.

NASDAQ says the trading halt is due to a UTP SIP quote dissemination issue.

(UTP stands for "unlisted trading privileges" and refers to the ability of other exchanges to trade securities listed on the NASDAQ. SIP stands for "securities information processor" and is the system that allows NASDAQ to send quotes for those securities to other exchanges.)

Shares of companies listed on the NASDAQ (not just options) – like Apple, Facebook, and Microsoft – have completely flatlined since shortly after noon.

The index isn't falling, it's just completely halted. In fact, NASDAQ futures, which trade on the Chicago Mercantile Exchange, initially fell when the trading halt was announced, but have since regained almost all of their losses.

Both the NYSE and the BATS Exchange have halted trading in all NASDAQ-listed Tape C securities.

The latest update from NASDAQ's website:

NASDAQ OMX PHLX, NOM, and BX System Update: Equity Trading in NASDAQ Listed Securities is resuming at approximately 15:25 ET . At 15:30 ET PHLX, NOM, and BX will purge all SQF quotes, after this time Market Makers may begin sending quotes. PHLX will resume trading in ALL option classes at 15:35 ET . Trading on NOM and BX Options will resume at 15:40 ET. Normal intraday $5 wide quoting requirements will be in place for all options markets.

According to CNBC, this sort of exchange-wide issue is unprecedented.

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