Eleven San Diego-area high schools were targeted by threats of violence Thursday, prompting lockdowns and police sweeps that turned up no immediate hazards, authorities reported.

The first local campus to receive a menacing call was San Ysidro High, which was phoned about 9:15 a.m. by someone who made a vaguely ominous claim that "something was going to happen" there soon, said Manny Rubio, spokesman for Sweetwater Union High School District. Officers searched the classrooms and grounds, then gave an all-clear about 11 a.m., he said.

Starting at about 9:30 a.m., meanwhile, threats about shootings or explosives were received at ten San Diego Unified School District campuses: Clairemont, Crawford, Kearny, Mira Mesa, Morse, Patrick Henry, San Diego and Scripps Ranch high schools, district spokeswoman Ursula Kroemer said. Point Loma and La Jolla high schools also received threats, San Diego Unified tweeted.