About 450 students were evacuated last night from their residence halls at the University of California at Davis after the police discovered explosive materials in a dormitory room.

Responding to a tip, campus officers searched the room and evacuated the surrounding buildings, directing students to a nearby dining hall, The Sacramento Bee reported today. Local law-enforcement agencies, regional bomb squads, the U.S. Bureau of Alcohol, Tobacco, Firearms, and Explosives, and the Federal Bureau of Investigation were quickly on the scene. Officers questioned four students and released three, the Bee reported.

The fourth student, Mark Christopher Woods, a freshman economics major, has been arrested on two felony charges, possession of chemicals to make explosives and possession of explosive materials on school grounds, the university said in a written statement.

Davis did not activate its emergency-notification system because officials there determined “there was no threat to wider campus safety,” according to the statement.

“We evacuated students as a precaution. We do not expect further disruption to the university,” Fred Wood, vice chancellor for student affairs, said in the statement. “We are confident that university police and other local law-enforcement agencies have the situation contained.”

Just before 8 a.m. today, university officials sent a campuswide e-mail message to inform students and employees of the situation. Classes and other activities are being held as scheduled. —Sara Lipka