According to a statement issued by the Anaheim Union High School District, the incident was described as an emergency that was "serious enough to transport the student to the hospital."
Classes were dismissed and everyone was sent home around 11 a.m., according to an email issued to parents.
"The family has requested that the name of the student not be disclosed as the incident is still under investigation," read the district's statement. "The family has asked for privacy during this time and to refrain from using social media in order to prevent rumors or misinformation that may turn out to be untrue or can be deeply hurtful and unfair to family and friends."
A spokesperson for the Anaheim Police Department told Eyewitness News the student did not succumb to injuries but remains in the hospital in critical condition.
The district said as more information becomes available, it will be released directly to parents.
Meanwhile, mental health professionals, counselors, and school psychologists are being made available to provide support to students as needed.
The National Suicide Prevention Lifeline provides free and confidential emotional support to people in suicidal crisis or emotional distress. If you or someone you know is in need of help, call 1-800-273-8255.