SAN DIEGO (CNS) - A pair of telephoned-in bomb threats disrupted classes and led to lockdowns at San Ysidro High School Wednesday.

A front-office secretary at the Airway Road campus received the first call about 10 a.m. from someone who apparently used some sort of computer-generated or recorded voice message to claim that an explosive device would detonate there within five minutes, according to San Diego police.

Students and staffers went to the school's football field and remained there while officers searched the grounds, finding nothing hazardous, said Manuel Rubio, a spokesman for Sweetwater Union High School District.

The emergency was called off after about 45 minutes, and things were back to normal by 11:30 a.m., according to Rubio.

About 15 minutes later, however, the school received another call about a purported a bomb at the campus, prompting a second security alert while police investigated, SDPD public-affairs Officer Matt Tortorella said.