Eight children were hurt, at least three of them critically, when a tree fell on a group of kids outside a summer day camp in Pasadena, the Associated Press reports.

According to KTLA, the victims, all of whom were between the ages of 6 and 8, were waiting to be picked up from a camp held at the Kidspace Children’s Museum when the 70-foot tree fell on Tuesday.

“I heard a tree crack, and then I turned around and I saw little kids running, then I saw the tree fall on top of the little kids,” a witness told KABC. “I ran over there with a bunch of parents and we just started going through the tree and the bushes and we started pulling them out.”

It was not immediately known what caused the tree to fall over.

“We are bringing out an independent arborist to investigate what could have caused this,” a fire department spokesperson told the Associated Press.

[Image via KABC]