A firefighter was killed and more than half a dozen people were injured when a building in Maine housing a center for people with disabilities exploded Monday morning.

The Farmington Fire Department responded a call about a "gas smell" at the administrative building for Life Enrichment Advancing People (LEAP), an organization that helps disadvantaged and disabled adults, just after 8 a.m., according to a statement from the Farmington Police Department.

A man works at the scene of a deadly propane explosion on Monday in Farmington, Maine. Jacob Gage / AP

"Upon arrival and while investigating the scene, the building exploded," the statement said.

One firefighter was killed, and at least seven other people, including six firefighters and a LEAP maintenance worker, were injured, according to police.

Maine State Police identified 30-year department veteran Captain Michael Bell, 68, as the firefighter killed in the explosion. His brother, Fire Chief Terry Bell, 62, also sustained serious injuries.

A deputy chief with the department was treated and released from the hospital while the other firefighters are being still being treated.

Police identified at the maintenance worker as 60-year-old Larry Lord, who was flown to Mass General Hospital in Boston and is in critical condition.

"I spent a year in Iraq and that's about the closest I can explain it. It was just total devastation," said Franklin County Sheriff Scott Nichols during a news conference Monday afternoon. "I've been in law enforcement 35 years — never seen anything like this before in my life except overseas. It was horrible."

LEAP is a private non-profit that was founded in 1980 and provides support to people with developmental, cognitive and intellectual disabilities, both in their own homes and in LEAP-provided and selected housing.

The organization's mission is to "empower people with disabilities to lead joyful lives with dignity, independence, and autonomy by providing comprehensive and individualized supports."

"Our hearts go out to anyone injured or impacted today," said a LEAP statement.

The LEAP building was "totally destroyed," and multiple homes in the area were damaged, police said.

Select Board Member H. Scott Landry said the LEAP building, which was recently renovated, was reduced to a hole in the ground.

"The new building is spread all over creation," he told The Associated Press.

He told NBC News that five minutes before the eruption, children were being picked up from a bus stop in front of the building.

Chief of Police Jack Peck said the explosion was so strong that people in the adjacent town of Wilton could feel it. Investigators say it might have been caused by a propane or natural gas leak.

Gov. Janet Mills said she was monitoring the incident.

"Our hearts go out to all those impacted by this tragedy, especially to the loved ones of the firefighter lost and others injured. I am grateful for the work of first responders who are at the scene and urge Maine people to avoid the area," Mills said in a tweet.

She later ordered the flags in the state be lowered to half-staff.