Nasdaq on Thursday 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 4:15pm GMT recommended traders route transactions to other exchanges.
The tech-rich exchange said on its 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% at 3,631.17 when trading was halted.