Work is being done to repair a window on police headquarters after a frightening incident this weekend.

A window at the Andrew Davidson building on 6th Ave. SE was shattered by a wrench that plummeted from the Bow Building under construction across the street.

The two kilogram wrench fell from the 45th floor of the building.

Police say it bounced off a concrete apron of police headquarters and smashed a main floor window.

The impact caused a 20 centimetre hole in the window and bent the tool.

No one was injured, but a passerby heard the sound of the wrench hitting the concrete and notified authorities.

Occupational Health and Safety is investigating.

This is the latest in a series of items falling from buildings under construction.

"Accidents do happen," said Ward 11 Alderman Brian Pincott. "It's what we do to minimize those accidents from occurring, or what happens when we have an accident. So every time there is an accident, it needs to be investigated, and this one will be as well."

Ledcor Construction says it has launched its own investigation.