The demolition of a former school will continue in Westmount, after part of the building collapsed prematurely on Wednesday.

Crews began tearing down the former Vanguard high school, at 175 Metcalfe Ave, two weeks ago, but on Wednesday afternoon a beam supporting the top floor failed.

Workers immediately evacuated the building and blocked off the area, with emergency officials expanding the cordoned-off area and ordering people living in a nearby buildings to leave as the top floor continued to crumble.

"When they started the demolition [Wednesday] the upper storey started to move," said Duncan Campbell, the Director General of Westmount.

He said the wider evacuations were necessary "just to ensure the structure was safe and there was no risk of further cascading onto the road."

Dr. Geoffrey Dougherty lives across the street in a home built in the 1890s, but was assured there was no risk of danger to his house.

He said he was worried about the demolition plans as soon as he learned of them.

"We expressed our concerns about the risk to the buildings of the construction process especially something so substantial as complete demolition and excavation and reconstruction," said Dougherty.

After an examination by the Workplace safety board (CSST) and the fire department, officials gave the demolition project permission to continue.

"To be fair to the fire department they erred on the side of caution which is exactly what we'd all want them to do," said Mayor Peter Trent.

"Once the engineer got here it was clear that indeed there was no danger and so people can go back."

Residents were allowed to return home on Wednesday evening.

When the building is demolished it will be replaced with a condominium tower.

Westmount's old Vanguard school collapses during demolition work pic.twitter.com/EFdj0jb72Z — Derek Conlon (@DConlonCTV) June 25, 2014