"Small scale demo activity has begun and will accelerate over the next days," First Selectwoman Patricia Llodra told television station WVIT, West Hartford, Conn.
"The process of demolition is incremental, staged precisely and executed carefully," she said. "There is no wrecking-ball action. It is rather a piece-by-piece, section-by-section removal."
The work site is shielded from public view to prevent anyone from taking photos or videos. Contractors taking down the school where 20 schoolchildren and six adult staff members were killed Dec. 14 have signed confidentiality agreements, WVIT said.
The massacre was the second deadliest mass shooting by a single person in U.S. history, after the 2007 Virginia Tech massacre, which left 32 people dead.
The Sandy Hook shooting prompted renewed debate about gun control in the United States and led to stricter gun laws in Connecticut, New York and other nearby states.
All parts of the elementary school, as well as the playground, driveway and sidewalks, will be pulverized or melted down so pieces of the tragedy can't be taken as souvenirs or sold to bidders on eBay, Llodra said last week.
The 28-member Sandy Hook School Task Force voted unanimously May 15 to demolish the school and build a new one on the same spot.
Town voters voted overwhelmingly Oct. 5 to fund the project with a $49 million state grant.
The entrance to the new school, scheduled to open by December 2016, will be relocated so people won't have to walk in front of a firehouse where anguished parents waited hours before learning their children were dead, the Los Angeles Times said.
While most residents say they want the school removed, a parent whose son was a first-grader at Sandy Hook when the mass shooting erupted said he considered the demolition a final surrender to the 20-year-old shooter, whose name is rarely said out loud in Newtown.
"The hardest thing I'm having to deal with is ... the feeling that we didn't just lose 20 children and six adults," Peter Barresi told the Times. "We're letting him take the building too, and he's winning."
The demolition is expected to be completed before the shooting's first anniversary in seven weeks.