Emergency responders in Maine were at the scene of a large fire and explosion at a lumber mill Friday in a small town in the state's scenic midcoast region where several people were injured. Waldo County officials said they are considering the fire and explosion a “mass casualty event.” They said at least five people were injured as of midday but a full assessment was not complete. Northern Light Eastern Maine Medical Center was treating one patient who was in critical condition, a spokesperson for the Bangor hospital said. The fire took place after the explosion at Robbins Lumber in Searsmont, a town of about 1,500 people about 95 miles (153 kilometers) from Portland , authorities said. Authorities said they are still investigating the cause of the blast. “We have dumped all of the resources from the whole county over to that area,” Waldo County 911 director Mike Larrivee said. Maine State Police and fire marshals are responding to the fire, state police spokesperson Shannon Moss said.…