Officers did not locate any weapons, and students are being allowed to leave, but police will remain at the campus as school lets out, San Jose police Sgt. Jason Dwyer said.
Someone had contacted police at 9:58 a.m. to report seeing a male, possibly a student, tuck a handgun into his clothing and then walk onto the campus, located at 1776 Educational Park Drive, Dwyer said.
The school went into lockdown mode as police surrounded the campus and began searching for the suspect.
"With limited information, we have to err on the side of caution," Dwyer said of the lockdown.
The caller gave police a description of the person with the gun, and police were trying to identify him.
About 30 patrol officers were dispatched to the school, Dwyer said. At any given time, he said, there are generally between 60 and 100 patrol officers on duty in the entire city.
"This is depleting our resources in the city right now," he said early this afternoon.
Police sent out a notice shortly after 2 p.m. saying that the lockdown had been lifted.
They said several "suspects" were searched, but that officers did not find any evidence of intended violence.