Michelle Le, 26, was last seen around 7 p.m. Friday as she headed to a parking garage at Kaiser Hospital in Hayward, police said. Her locked Honda SUV was later found a few blocks away.
She had a break from her clinical rotation and had told classmates she planned to drive to Reno, Nev., later that night to visit friends.
Police believe Le had her cell phone with her when she disappeared, but calls to the number have gone unanswered. Investigators also were checking several surveillance cameras in the parking structure.
Hayward police Lt. Roger Keener said detectives were looking into a possible connection between Le's disappearance and a similar case in Fairfield, about 55 miles away, that remains unsolved.
Le was about halfway through a 12-month accelerated bachelor's degree program at Samuel Merritt University in Oakland, said university spokeswoman Elizabeth Valente. The program combines classroom work with clinical training, which is what Le was doing at the time of her disappearance, Valente said.
The Associated Press contributed to this report.