The fire tore through Sam Auto Repair shop on the corner of Ronkonkoma Avenue and Portion Road. Fire officials say it started around 12:30 p.m.
Ronkonkoma Fire Chief Kevin Murray says the fire started in one of the cars at the shop.
"The owner of the business was working on a vehicle inside the garage," says Murray. "At some point, while working on the vehicle, the fire broke out."
Murray says flames caused the building's roof to collapse, and wrecking crews knocked down walls that were unstable.
Sam Auto Repair is housed in a building that was once known as Newton's Garage. Residents say it's one of the oldest buildings in Lake Ronkonkoma.
"Historical Newton's Garage. I've lived in Ronkonkoma my whole life and I'm very sad to see it gone," says Annette Dale. "But nobody got hurt I hope."
Newton's Garage was opened in 1921.