An 11-year-old girl was killed Monday morning and three others injured when a tree fell on them at a southern Indiana campground, the Perry County sheriff said.

Isabelle Meyer died after suffering head and abdominal injuries, authorities said.

Deputies responded to a 911 call about 11:30 a.m. and found four people pinned beneath a fallen tree.

The other three victims, a 10-year-old girl and two women, were taken to area hospitals. The 10-year-old has since been released.

The victims were hiking on a gravel road on a fairly steep incline and were on their way down when the tree fell in what Sheriff Alan Malone said at a Tuesday news conference was "very bad timing."

Malone said it was uncertain why the tree, which he estimated to be about 40 feet tall, fell. He said the ground was saturated from recent rainfall, but there were no severe weather warnings in effect.

“We had an amazing response yesterday,” the sheriff said at the news conference, tears filling his eyes. “Unfortunately, a little girl died.”

He added: “We’re prepared for everything, but when you actually roll up on a scene — it’s hard, it’s tough. Especially when a child is involved.”

Camp Koch is operated by the Girl Scouts of Southwest Indiana, according to the sheriff.

The scouting organization confirmed the "tragic death" of one of its members and said it has closed Camp Koch while the incident is being investigated.

"There is nothing Girl Scouts takes more seriously than the safety and welfare of our girls — at camp and during all Girl Scout activities," Girl Scouts of the U.S.A. told NBC News in a statement. "We grieve this terrible loss as one. At this difficult time, please grant the victims and their families privacy."