More than 3,000 students in a Californian high school were evacuated Wednesday morning while authorities investigated a bomb threat on the campus.

Students in San Clemente High School were told to leave classes around 9 a.m. local time (1600 GMT) on the first day of school. All the student were released from school by 1 p.m. local time ( 2100 GMT), while searching for explosives was continuing.

Some 180 staff of the school were also evacuated.

The Sheriff's Department of the Orange County began searching the campus room-by-room on receiving information about a written threat that explosives were placed in the school.

Local police said that the written threat was found in personal belongings of a missing Navy corpsman, who was identified as 22- year-old Daniel Morgan.

No further information is available for Morgan and other details, such as the motive, for the time being.