Someone is torching buildings in Manteca.

The latest incident was on Thursday at 11:15 a.m. when flames from a suspicious origin engulfed at 20- by 80-foot outbuilding behind a vacant home on North Union Road brought 11 firefighters, two engines and a rescue unit to the scene.

Firefighters immediately went into an aggressive attack mode with the flames coming from a small living quarters at the front of the structure.  A sign that warned of video surveillance led to a camera that had appeared to have long been disabled.

The alarm and 911 call had been turned in by a construction worker who was driving by the scene in his pickup truck and spotted the smoke coming from the building.  Shoppers at Raley’s Grocery Store across the street and at O’Reilly’s Auto Parts store lined up to watch the fire.

The outbuilding apparently served as a work shop with a bench and tools left behind.  The structure had been locked and firefighters were forced to cut chains and locks on its doors.

Battalion Chief Dave Marques confirmed the suspicion of possible arson in the blaze and estimated the loss at $10,000 to the building and another $5,000 for a ski boat that had been parked inside.  Firefighters were on the scene for nearly an hour including a short mop up once the fire was out.

The string of suspicious arson fires plaguing Manteca include:

• Last month four transport vans were torched at East Union High for a loss of $100,000

• Last month the second fire this year and fourth fire in two years was set at the former agricultural commissioner’s office on Moffat Boulevard

• In July someone tried to burn down the Chili’s Restaurant by starting a fire near the rear door. The damage was placed at $100,000.

• In late May a boarded up two-story house in the 1700 block of North Main was destroyed with the loss estimated at $200,000. Arson was suspected in that fire as well.

• In June of 2011 a three-alarm fire topped $1.1 million in losses to the complex in the 700 block of North Main Street that housed Rocko’s Sports Bar among other businesses.

• Two other vacant buildings were burned along Moffat Boulevard last year.