UPLAND (CBSLA) – Upland High School in San Bernardino County was placed on lockdown for several hours Friday due to an unspecified threat.

The lockdown at the school, located at 565 W. 11th St., took affect before 10:20 a.m. The Upland Unified School District superintendent’s office confirmed that Upland police were sent to the school to investigate and that parents had been notified.

Police were informed as a precaution, the district said. The Press-Enterprise newspaper reported that the threat was based on suspicious text messages.

Upland police were also aware of a photo on social media that showed a person in a gas mask that may be connected to the threat, the newspaper reported.

The lockdown was lifted at around 12:30 p.m.