Classes at Centennial High in Corona were canceled Tuesday, Sept. 8, after someone phoned in a bomb threat and police discovered two suspicious backpacks.

Nothing harmful was found in the backpacks, and police left the school about 8:15 a.m., Corona police Sgt. Paul Mercado said. Even though the school was declared safe, classes were not held Tuesday, Mercado said.

But extracurricular activities, including athletics, were going on as scheduled, Corona-Norco Unified School District spokeswoman Evita Tapia Gonzalez said.

Centennial has about 3,350 students and 150 staff members.

About five hours before the bomb threat was made, a hazardous materials team responded to the school because of fumes being emitted by cleaning equipment. The incidents were unrelated, officials said.

About 12:45 a.m. Tuesday, a male called the non-emergency police dispatch number and said there were two pipe bombs in a backpack on campus that were going to blow up Tuesday morning.

Police went to the school, and a K-9 alerted police to a locker where a backpack was found, Mercado said. Another backpack was found near the administration building, an unusual location for a backpack to be left, he said.

The Riverside County Sheriff’s Department’s bomb squad found that neither backpack contained any explosives, Mercado said.

Corona police are still trying to determine whether it was a serious threat or just a hoax, Mercado said. No arrests had been made by late Tuesday afternoon.

Police asked anyone with information about the bomb threat to contact Officer Michael Placencia at 951-739-5670 or Michael.Placencia@DiscoverCorona.com.

The school district alerted parents and students that classes would be canceled about 7:05 a.m. through emails and text messages. No students showed up for the 7:40 a.m. scheduled start of classes, Tapia Gonzalez said.

The district does not cancel classes after every threat, she said. But the nature of the threat and discovery of the backpacks, as well as the uncertain amount of time it would take to clear the campus of students and staff, led school and police officials to decide to cancel classes.

Shortly after 9 a.m., Centennial’s parking lots were nearly deserted, though one Corona police cruiser stood in a side lot. Police and school officials referred inquiries to the school district at 951-736-5154.

Instead of adding a day to the school year, the district will petition the County Office of Education and the state to receive the money the school would have received for each student if classes had been held, Tapia Gonzalez said.

Staff writer Alicia Robinson contributed to this report.