High winds and a fierce thunderstorm left people cleaning up in the City of Vaughan Tuesday morning.

A construction site at 9000 Keele Street near Langstaff was toppled by wind gusts that reached 100 km/h Monday afternoon. Many new homes being built next to an office building were knocked down and debris scattered about, creating a frightening situation for people at work next door.

Paul Morgan was looking out his office window as the destruction began.

"And (I) saw debris flying in the air, large pieces of plywood and pieces of two-by-four," Morgan said.

"I saw my car get struck by a piece of wood and came out and noticed the building had collapsed behind us."

Inside a heavy excavator on the construction site, Remo Luciani said everything started to spin around him.

"All of a sudden the wind was so high ... and I turned around and I see plywood flying everywhere and the building come down," Luciani said.

He added that "three or four" lightning bolts hit a nearby hydro pole, setting it ablaze.

Environment Canada is saying "high gusts" were behind what happened in Vaughan.

"From the appearance of this damage everything seems to be shoved over towards the east," Geoff Coulson said.

"In other words, sort of confirming the fact that it likely was a very strong wind gust coming from the west that pushed the structure over."

Construction workers at the site spent much of Tuesday cleaning up instead of building the new homes.

Meanwhile, hundreds of people north and east of the Greater Toronto Area were waiting for electricity to be restored Tuesday morning.

Reports say about 17,000 Hydro One customers lost power in areas stretching from Parry Sound to Arnprior.

Hydro One crews went out right away to begin restoring electrical service. Work continued through the night and the power utility hoped to get all customers back online by between noon and 4 p.m. Tuesday.

With a report from CTV's Galit Solomon and files from The Canadian Press