Kittery Fire Chief Craig Alfis speaks to media outlets as emergency personnel respond to Building Blocks Learning Center in Kittery for reports of carbon monoxide incident on Wednesday evening. Derek Davis/Portland Press Herald

The carbon monoxide poisoning that hospitalized 11 people in a Kittery day care stemmed from the improper use of a propane-powered concrete saw in the same building, the state fire marshal’s office said.

Workers were using the saw in a nearby suite that was under construction, and smoke detectors near the saw were covered up, Department of Public Safety spokesperson Shannon Moss said. The saw is not supposed to be operated indoors, she said.

Alarms didn’t appear to be going off when first responders arrived, but the fire alarm system in the building appeared to be functioning normally, Moss said.

State law requires all child care facilities to be equipped with smoke and carbon monoxide detectors. It wasn’t clear Thursday if the building was in compliance.

Seven adults and children were brought by ambulance and four went independently to Portsmouth Regional Hospital on Wednesday afternoon after becoming sick from potential carbon monoxide poisoning at the Building Blocks Learning Center on Route 236. They were all released later that night, a hospital spokesperson said.

There were 27 children and 10 staff members inside the child care center when staff noticed an odor and people feeling sick, the Office of the State Fire Marshal said on Thursday. The providers evacuated everyone and called the fire department around 3:19 p.m., when all Kittery police and fire units and other agencies in the area responded.

“It is important to note that day care providers of the Building Blocks Learning Center recognized a problem and took action,” State Fire Marshal Shawn Esler said in a written statement. “They evacuated children and staff to safety and notified the fire department as soon as they recognized something was wrong. Their quick response, the professionalism of the Kittery Fire Department, and the medical expertise of the Portsmouth Regional Hospital helped prevent a tragedy.”

Authorities were on the scene until after midnight to determine the cause of the gas. Investigators found a propane-powered concrete saw, which was being operated in a separate suite inside the building, which includes several businesses. The suite, which was not affiliated with the day care, was under construction.

The unit in which the saw was operated had a valid building permit from the town, Kittery spokesperson Courtney Grugnale said. That permit has been placed on hold while the Kittery code enforcement team conducts a review, she said.

NorthPoint Construction Management, a New Hampshire company, applied for that permit, Grugnale said.

The company did not immediately respond Thursday night to questions left in a voicemail and messages sent through its website regarding its permits, use of the saw or why the detectors had been covered.

The carbon monoxide from the saw’s exhaust could have infiltrated the day care through an HVAC duct or above a suspended ceiling that had been removed during construction, Moss said.

Investigators will consult with the alarm company to determine whether the alarm system has the capability to detect both carbon monoxide and fire. The fire marshal’s office will continue to investigate the incident, said Moss, who declined to say whether charges will be filed.

Staff Writer Daniel Kool contributed to this report.