By AARON PARSEGHIAN

A tractor-trailer brought down high-voltage power lines in Waltham, Massachusetts on Friday, sparking a fire that damaged three vehicles, including at least one school bus van, and temporarily knocked out power to hundreds.

The incident happened just before noon near Totten Pond Road, when the truck caught low-hanging power lines while a witness said they were trying to back into a loading dock.

The snag sent the live cables crashing into a nearby parking lot, where they ignited multiple vehicles.

"I heard an explosion, it almost sounded like a gunfire, like something exploding," said Marilyn Ross, who was driving by and recorded thick black smoke pouring from the scene.

Waltham firefighters said the energized lines initially prevented them from extinguishing the c

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