Torontonians saw an unusual sight Thursday afternoon as the CN Tower was engulfed in smoke, as part of a rehearsal for the Pan Am Games opening ceremony.

Ashton Lawrence tweeted this stunning image of smoke pouring from the tower.

A <a href="https://twitter.com/hashtag/TO2015?src=hash">#TO2015</a> Pan Am warm up? <a href="https://twitter.com/hashtag/CNTower?src=hash">#CNTower</a> <a href="http://t.co/S8ldhGgOPL">pic.twitter.com/S8ldhGgOPL</a> —@Ashton_Lawrence

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.

Toronto Fire confirms the CN Tower smoke is Pan Am pyrotechnics. They were aware of it - just not perhaps the extent of the smoke. —@wisem

The fireworks set off from the CN Tower are part of the dress rehearsal for the Pan Am Games Opening Ceremony, as announced earlier today. —@TO2015

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.

Wow, before you start testing fireworks for tomorrow's Pan Am Opening...you may wanna warn people. <a href="https://twitter.com/hashtag/CNTower?src=hash">#CNTower</a> <a href="http://t.co/5d23dWEIbp">pic.twitter.com/5d23dWEIbp</a> —@MonikaPlatek

I guess that's one way to get people to pay attention to the Pan Ams <a href="https://twitter.com/hashtag/CNTower?src=hash">#CNTower</a> —@JonGatehouse