A dozen people were injured when a tree fell on a Diablo Valley College football field during a graduation commencement ceremony Friday evening.

The incident happened at 6:54 p.m. toward the end of the ceremony in Pleasant Hill, according to a statement from the college.

A tree fell adjacent to the football field, and bystanders who were watching the ceremony were hit by the tree. It is not immediately clear what caused the tree to fall down.

Approximately 12 people were treated for injuries and two people were transported to local hospitals for treatment. Their conditions have not been released. The others were treated onsite and released, while another person went to the hospital on their own, the college states.

Emergency responders and police services were already on site per the college’s standard event protocol and quickly treated the injured. The college’s maintenance staff removed the tree after the emergency response.

An evaluation of the incident has begun and will continue in the upcoming days.

In a statement, college officials said their thoughts are with the, “individuals and families affected by this incident, and wish those injured a speedy recovery.”

“The safety of our students, employees and visitors to our campus is our top priority,” the college said. “We deeply regret that this incident occurred during this milestone occasion.”

Diablo Valley is a community college in Contra Costa County with campuses in Pleasant Hill and San Ramon.