A four-alarm fire tore through a commercial building in Brooklyn early Sunday morning, authorities said.

Fire officials said 40 units and 170 firefighters responded to the blaze in two businesses – an auto-body repair shop and a motor repair shop – within the one-story building near Schenectady Avenue and Glenwood Road in East Flatbush around 2 a.m.

The fire “got really advanced prior to our arrival,” said FDNY Chief Roger Sakowich after the flames were extinguished. “We believe it started in either one of the two shops on what we call the left side of the building.”

Both shops were unoccupied at the time. A third business within the warehouse was not affected by the fire.

Firefighters fought the flames from the outside after they discovered the presence of compressed gas tanks inside.

The fire was under control within approximately three and a half hours, Sakowich said, at which point a fourth alarm was added for “relief purposes.”

No injuries were reported and the cause of the fire is under investigation.