EL CAJON, Calif. -- Grossmont High School was placed on lockdown Thursday morning because of police activity in the area, but no students were directly threatened, district officials said.
El Cajon police lifted the lockdown around noon -- three hours after it went into effect -- as they were unable to substantiate any threat to students, Catherine Martin, spokeswoman for the Grossmont Union High School District posted on Twitter. Classes resumed as scheduled.
While the campus was secured, classroom doors were locked, but instruction continued, according to Martin.
"Students are safe in classrooms," Martin tweeted at 8:57 a.m.
Customs agents were at the school to assist police officers and sheriff's deputies with canine searches of about 20 buildings on the 66-acre campus, Martin tweeted.
In subsequent tweets, Martin reported that El Cajon police were investigating a "possible threat" to students but said the pupils were safe and secure and later clarified "no students at Grossmont High School were directly threatened."
Classrooms are equipped with crisis buckets that include supplies such as snacks and water, Martin said.
The nature of the police activity in the area wasn't immediately known.