An 18-year-old Gunn High School student was arrested Thursday for bringing a weapon to school.

Weston Healy was taken into custody shortly before 3 p.m., following a campus lockdown that was called just as the school day was ending around 2 p.m. and which lasted about 45 minutes.

Healy was initially seen taking an Airsoft rifle out of his car, which was parked on campus, and placing it in the trunk, according to Police Lt. Sandra Brown.

Airsoft rifles shoot BB-sized plastic pellets.

It is a felony to possess a knife, gun or other weapon on campus, Brown said. Campus includes not just the academic buildings but also the parking lot and athletic fields, she added.

As of 3:30 p.m., Healy's parents were at the school talking to police and school officials, police said.

Other Gunn students were ordered to stay in the classrooms and other buildings at around 2:05 p.m. by police, who searched the campus.

Students were released from the school shortly before 3 p.m., and several said they had not been informed about what was happening.

Police and school officials were themselves scrambling to determine what was occurring, according to reports.

Gunn issued an e-mail statement to families at 3:56 p.m. saying the school had "experienced a Code Red as a safety precaution."

"At no time were students or staff in danger," the Gunn statement said. "Students and staff did an excellent job of following the Code Red procedure and the Palo Alto Police Department's response was immediate and extremely effective."

Brown said officers arriving at the scene found the unoccupied vehicle and decided to "take no chances" and order classrooms locked. A police SWAT team also arrived on campus.

Students reported that they were only told it was a "Code Red" alert.

Arriving parents were diverted to Alta Mesa Cemetery across Arastradero Road from Gunn while police and school officials concentrated on room V9 in the portables section of the school.

Other parents waited in cars along Miranda Avenue and on Arastradero Road until cones barricading the campus entrance were removed. Many were on cell phones attempting to reach their children inside the school.

One student reported that desks has been pushed up against the inside of the door of the classroom.

As students poured out of Gunn following the lockdown, the campus still swarmed with police and students said the cause of the disturbance had not been clarified.

One student said she had been confined in the school's main office with staff, while other students said they had been held in classrooms or the school's library. They were unsure of the cause of the disturbance, or whether those detained were Gunn students or outsiders.

The following comment was e-mailed to the Gunn community by school officials:

"This afternoon as students were leaving class, Gunn experienced a Code Red as a safety precaution. There was a report of a gun on campus that had been seen in a car. Police were called immediately and worked with school staff to determine that it was a non-lethal air soft gun.

Police are investigating and are talking with the individuals involved. At no time were students or staff in danger. Students and staff did an excellent job of following the Code Red procedure and the Palo Alto Police Department's response was immediate and extremely effective."