The Androscoggin Mill in Jay Credit: Courtesy of Verso Corp.

Officials at a Maine mill say a gas leak Wednesday forced an evacuation of the building and sent four contractors to the hospital.

Verso Androscoggin Mill spokeswoman says Kathi Rowzie says a valve was left open at the Jay-area mill, releasing chlorine dioxide gas. The Sun Journal reports no one was injured and the contractors were hospitalized as a precaution after the gas was detected by sensors.

Rowzie says employees evacuated the mill Wednesday morning. Employees later returned to work that day after the valve was closed and the air tested clear.

Officials say an incident report, which is standard protocol at the mill, will be submitted by Friday.