Ashton Lawrence tweeted this stunning image of smoke pouring from the tower.
Toronto Fire spokesman Stephen Powell confirmed that the cause of the smoke was a pyrotechnics display related to the Pan Am Games.
A Pan Am games spokesperson confirmed that the fireworks were set off as part of a dress rehearsal for the Games' Opening Ceremony.
Power told CBC's Mike Wise that they were aware something was planned to take place at the tower, but they didn't know about the amount of smoke that ended up billowing from the observation deck.
Not everyone got the memo about the rehearsal, though. Any short-term panic Torontonians had at the sight of the engulfed tower was quickly extinguished, turning some of their incredulity at the Games instead.