Authorities are investigating why a planned building demolition in downtown Vancouver went awry on Thursday, toppling two separate walls onto busy streets. Miraculously, no one was injured.

The building, which previously housed the William Davis Centre for Acting, was being demolished early Thursday evening at the corner of Hornby and Helmcken streets when the north wall collapsed into the street.

Hundreds of pounds of rubble spilled onto the road, shooting clouds of dust and debris into a car stopped at a nearby intersection. Shortly after, a second wall fell, toppling a light standard and narrowly missing a flag person standing on the road.

Both the City of Vancouver and WorkSafe BC -- which can fine the developer or the demolition company up to $519,000 -- are investigating. Crews were at the scene Friday morning trying to determine what caused the collapses.

Pending the outcome of the investigation, Vancouver's chief building official Will Johnston said the city has "shut the site down and ask that they stop construction."

Global Excavation and Demolition, the company hired to tear down the building, declined to comment.

The property is the future location of high-end condo development Hornby Residences. Project manager Cairan Mulhall said the lanes surrounding the building were blocked off during the demolition, but that the city did not allow crews to close off the street entirely.

"The flag person during the risky part of the excavation did block traffic as much as possible," Mulhall said. "Obviously there was an incident and things went wrong. The plan was for the walls to fall inward and not outward."

But damage control may be difficult; footage of the first and second collapses has already gone viral on YouTube.

With a report from CTV British Columbia's Shannon Paterson