Ken Reese, who lives on Howell Road near the building, said he was turning onto Mount Aetna Road when he saw the sky light up, and his wife pointed and said lightning had just hit the white building.
Hagerstown firefighters discovered the fire while responding to an automatic alarm at a business across the street, the fire marshal said.
Firefighters from Funkstown, Mount Aetna, Hagerstown, Halfway, Longmeadow, Special Operations 20, Air Unit and Rehab Unit responded to the fire.
The building at 1190 Mount Aetna Road houses 10 professional offices, including the physical therapy center, owner Stephen Ryan said. The center was holding a free seminar on nutrition when the fire started, marketing director Blakeley Jackson said.
Tree causes damage
A tree fell across Bester Street during heavy winds around 6 p.m., damaging a house and crushing a pickup truck, Hagerstown Fire Department Battalion Chief Randy Myers said.
The tree brought down power lines and pulled over a utility pole, Myers said.
Officials blocked off the 200 block of South Locust Street while the city turned off power to the downed lines. The portion of the tree blocking Bester Street was scheduled to be cleared this morning, and public works manager Eric Deike said the street should be reopened today.
Bester Street was still closed this morning, Sgt. Elmer Hurd of the Hagerstown Police Department said.
Tara Wilson said she saw the tree fall and heard a loud "boom" as the tree appeared to shift the whole house.
"It looked like a twister came through," said Scott Hines, who also lives on Locust Street. "It was raining pretty good, and all of a sudden the wind just whipped up like crazy. There were trees falling and limbs flying through my yard."
At one point during the storm, five city traffic signals were out, a Hagerstown Police Department dispatcher said. Washington County emergency dispatchers received 11 calls about downed power lines, mostly in the city.
The city had scattered power outages throughout the West End and North End, city spokeswoman Karen Giffin said. About 300 city customers lost power, Giffin said, but all were expected to have it back by today.
In the Eastern Panhandle of West Virginia, the storm knocked out power to 4,100 Allegheny Power customers in Martinsburg, W.Va. That number later dropped to 1,700 customers who were expected to have their service restored by about 10:30 p.m., Allegheny Power spokesman David Neurohr said.
The outages occurred in the north, central and southwest sections of the city, Neurohr said.
Streetlights and stoplights along at least four blocks of Queen Street and even more on West King Street to Winchester Avenue were out.
A transformer fire reported near Faulkner and Winchester avenues knocked out electricity to areas south of West John Street.
Berkeley County emergency dispatchers said they alerted authorities to dozens of 911 calls, including reports of wires and trees down and an air conditioner fire.
Franklin County, Pa., 911 dispatchers reported limbs and wires down on both Williamsport Pike and Redwood Drive in Antrim Township.
Staff writers Dave McMillion, Matthew Umstead, Erin Julius and Jennifer Fitch contributed to this story.