A large glass pane has fallen out of the SAP building on the corner of Queen and Wyndham streets.
There were people underneath but no one was hurt, "thank god," one witness said.
She said the window broke as it fell, rather than break on someone.
She said the pedestrian light had only turned green a few seconds before the glass fell. "Otherwise, it would have fallen on top of someone."
Sergeant Dan Weir said fire services had been dealing with securing the remaining glass.
"All the glass has been removed now and traffic has opened up again," he said.
No injuries were reported.