For the second time in two days, San Ysidro High School classes were disrupted after receiving a recorded bomb threat.
School officials said a Skype call came in at 7:39 a.m. warning that there was an explosive device on the Airway Road campus.
This time, the recording said there was 65 pounds of dynamite on campus that would detonate at approximately 8:30 a.m., officials said.
School officials and police say the threat was very similar to one made Wednesday at the same campus.
Principal Hector Espinoza said the bomb threats are the first in the school's history.
"They're similar messages. They are automated. It's not speaking to a specific person," Espinoza said.
Police dogs searched the campus before students were returned to class by 9:45 a.m.
Cecilia Martinez stopped by the school to pick up her 15-year-old daughter who was scared.
"It was a threat but what if something happened for real," Martinez said.
On Wednesday, students were evacuated to the football field after the school's secretary answered the phone and heard a recorded message that stated a bomb could go off in a few minutes, according to the San Diego Police Department. No device was found.
On Thursday, administrators moved the entire study body and staff into the gym and explained the situation while police swept the school.
"We can't ignore [the threats] obviously but we take the necessary precautions to make sure we're 100 percent guarantee that there are no explosives or bombs on campus," Espinoza said.
San Diego Police were expected to stay on campus throughout the school day as an extra precaution.
Espinoza said investigators were working with Oceanside Police to see if the person behind the San Ysidro HS threats was responsible for a similar threat to Oceanside High School Wednesday afternoon.
He said the source of the threats would be prosecuted to the fullest extent of the law.