Trading on the Nasdaq OMX PHLX - as the former Philadelphia Stock Exchange is known - was expected to resume at 12:40 p.m. today after being halted for an hour and a half because there was smoke in the building.

The PHLX, at 1900 Market St., said that employees were evacuated and that essential staff had been relocated after trading was halted at 11:05 a.m.

The company said in a statement that the smoke had been cleared from the floor, and that the origin of the smoke had not been determined.

All other operations by Nasdaq, which bought the exchange last year, were said to be operating normally.