Work crews had already been working at removing the glass panels under a city order issued 12 days ago when two tempered panels came loose and dropped from the 18th and 35th floors, the Toronto Star reported.
The first incident happened earlier this year at the downtown Murano buildings. One tower is 45 stories high and the second is 37 stories.
The builder, Lanterra Developments, says on its Web site the "intricately glass design encasing the towers portrays the glass artistry of the [Italian] island of Murano."
No injuries have been reported in any of the incidents, but each time police have been forced to close the arterial Bay St. to traffic and pedestrians.
Tower residents have been told their balconies are off-limits and that removal of all glass panes could take as long as two months, the report said. It wasn't known how long replacement work would take once the thousands of panels were all down, the Star said.