Nasdaq today suspended trading of all stocks and options due to technical problems.
The exchange halted trade in all "Tape C" securities, which includes options and securities. A message from Nasdaq around 1615 GMT recommended traders route transactions to other exchanges.
The tech-rich exchange said on it website that it intends to resume trading "at a time to be determined." The exchange said customers wishing to cancel orders could do so.
A spokesman for the Securities and Exchange Commission said the US securities regulator was monitoring the situation and was "in close contact with the exchanges."
Nasdaq attributed the shutdown to a problem with its SIP system, which interfaces with other exchanges on stock quotes.
"We're still investigating this. It's a technical problem on the UTP SIP system, halting all the Nasdaq options" said Nasdaq spokesman Ryan Wells.
The Nasdaq index was up 0.87 per cent at 3,631.17 when trading was halted.
