It happened around 5:55 a.m. Friday at the Karamoor Estate Vineyard & Winery on the 6100 block of Butler Pike.
The Country Flower Shop is nearby the winery, and that's where Ted Risnychok was when he saw the fire.
"We looked out at our windows this morning and saw the flames at the front of the building and coming through the roof," Risnychok said.
The barn is owned by philanthropists Nick and Athena Karabots, major donors to a number of institutions including the Franklin Institute and Children's Hospital of Philadelphia's Pediatric Care Centers.
"Multiple agencies around the area, close to 100 firefighters on scene, establishing water supply and having a difficult time with that, but were able to get the fire contained as it is right now," Whitemarsh Township Fire Marshal Nick Weaver said Friday morning.
For hours, firefighters blasted water at the barn. No injuries were reported.
The building was under construction. The plan was to open the barn as a wine bar and tasting room.
The strong stone exterior stood with extensive damage to the inside.
"This was a project under construction. It was supposed to be a wine bar for Karamoor Farms, they have a winery on site. It was projected to open after early 2021," Weaver explained.
Risnychok added, "I watched it progress over the years as they were refurbishing the barn for the Karamoor Estate Winery, and they were moving right along, and everything looked absolutely gorgeous."
Karamoor Estate Vineyard & Winery posted a message to its Facebook page late Thursday morning:
"Our Karamoor Estate bottle, still stands tall and strong! Thank you for all of your kind and encouraging words. We are so fortunate no one was injured and it appears the damage stayed within the walls of the new tasting room walls and close perimeter. My heart breaks for the Karabots. Any of you who have been to Karamoor Estate or know the Karabots, understand this has been a labor of love and as I've mentioned to many...good things come to those who wait. It IS going to be magnificent. Stay safe and healthy and please know we appreciate each and every one of you and your continued support."
The cause of the fire is under investigation.