Two young girls who were seriously injured Friday when the snowmobile they were riding hit a group of trees were being supervised at the time, according to a spokesman for the Maine Department of Inland Fisheries & Wildlife.

The girls, ages 9 and 10, were riding a 1988 Ski-Doo by themselves and without helmets when they lost control of the snowmobile, causing it to hit trees in New Portland.

Mark Latti of Inland Fisheries & Wildlife wrote in an email Monday an investigation into the incident was ongoing. He did not say who was monitoring the children when they crashed.

Latti said later that investigators were still trying to determine which girl was operating the snowmobile on land off Millay Hill Road. It was not clear if the girls were driving on land owned by their family or if it was someone else’s property.

The girls suffered head, chest and back trauma and were rushed to Franklin Memorial Hospital in Farmington. They were then were flown by a LifeFlight of Maine helicopter to Maine Medical Center in Portland, according to officials.

The 10-year-old girl was released from the hospital Saturday, while the younger girl was still hospitalized Monday.

Maine law allows a person as young as 10 to drive a snowmobile if the child is accompanied by an adult, according to Latti. A provision exists, however, that there is no age restriction if a snowmobile is being operated on land owned by a child’s parent or guardian or land where permission to ride has been granted to the parent or guardian.

The Maine Warden Service, NorthStar Ambulance, the Franklin County Sheriff’s Office and New Portland Fire Rescue responded to the crash.