A Marine recruit based out of San Diego, California, was pronounced dead at 11:43 a.m. Sunday, according to Marine Corps officials.

The cause of death is still unknown, but the recruit was rushed to a hospital off base after experiencing a medical emergency late Friday night. A drill instructor at the depot had come across the recruit experiencing a medical problem and administered CPR until first responders arrived, according to the Marine Corps.

The recruit was in critical condition after arriving at the off-base hospital.

“Supporting the recruit’s family is our top priority and we continue to work closely with them during this most difficult time,” Brig. Gen. William Jurney, commanding general of the San Diego recruit depot, said in a command release.

The cause of the medical emergency is still unknown, but Marine officials at the depot stated the recruit was being monitored for “ongoing physical health issues” before the incident occurred.

The name of the recruit is being withheld until next of kin notification. Medical officials are working to determine the cause of death.