As the embers cooled Tuesday on the scorched ground of 100 Chase Farm Road in Hopkinton, the cause remained unknown a day after a fire destroyed a garage and spread across five acres of brush and fields.

Fire chief Jeff Yale said the fire marshal’s office is leading an investigation into what started the blaze.

Yale, who was present at the scene along with first responders from around a dozen towns, said Tuesday that the incident was a three-alarm fire that also destroyed three vehicles and damaged a fourth.

The fuel inside the vehicles and propane tanks inside the garage led to explosions that allowed the flames to spread, Yale said.

“The unfortunate part of this is that this time of year, like yesterday, there’s a high fire danger,” he said. “There were explosions and floating embers still on fire, radiant heat, not to mention the location on a hilltop. The slight wind condition didn’t help us either. There was both wind and dryness. No one started that brush fire. It’s just a result of the building fire.”

The 56-acre property contains many structures, including a shed, patio and barn. The house, a white Colonial dating to 1776, was not harmed by the flames.

Yale urged vigilance to anyone who should encounter a brush fire.

“Move what you can,” he said. “Report them as soon as possible to us so we can rectify those issues as soon as we can.”

Rachel Wachman can be reached at rwachman@cmonitor.com.