The S&P/TSX Composite Index was last seen down 338 points mid-morning with shares in base metals and information technology posting the biggest losses, and bond yields rose.
Base metals were down 3.3% with gold and other metals prices falling, followed by information technology, down 1.0%.
The energy sector was up 1.0%, boosted by higher oil prices.
US 10 year bonds rose 5.056% mid-morning after the release of S&P September flash PMIs. Flash US Composite PMI Output Index jumped to 58.4, from 56.0 in August, a 62-month high.
In stocks, AGF Management (AGF-B.TO) shares fell 6.5% to CA$17.32 on last look, after it reported adjusted third-quarter earnings of CA$0.49 per share, missing FactSet estimate of CA$0.58 per share.