Those injured include five firefighters and a maintenance director of the building, said Rep. Scott Landry.
Mills said the cause of the incident is now under investigation.
"It's a war zone here", Landry said from the scene.
"My stepdad was first on scene after the explosion", he told CNN.
The Latest: 5 remain hospitalized after propane explosion | Fort Worth Star-Telegram
One person is reported dead after a Monday morning explosion on Farmington Falls Road in Farmington.
The explosion occurred after officials were investigating a propane smell at the LEAP facility.
The blast injured four other firefighters, including the town's fire chief; one employee of the nonprofit center; and one ambulance worker, officials said.
The blast around 8:30 a.m. was heard for miles and had enough force to blow a vehicle across an intersection.
Video of the aftermath of the explosion is being shared on social media, showing clouds of smoke and debris in the air.
The Franklin County Sheriff's Department in ME says firefighters are responding to a building explosion that rocked the town of Farmington and a county sheriff says there are injuries. The building is the central office for LEAP Inc., which provides support for people with developmental, cognitive and intellectual disabilities.
Kim Hilton, who works at the nearby University of ME at Farmington, told the Associated Press that the blast rocked her building, too.
The conditions of the injured firefighters weren't immediately known.
Potential ban on vaping products could hurt local business in CT
The FDA is now finalising its plans to remove flavoured e-cigarettes from the market within the next 30 days. Professor John Newton, also of PHE, added: '[We have] always been clear that vaping is not without risks.