The Portland Police Department is investigating what appears to be a hoax 911 call about a possible gunman at Portland High School.

The school was placed into lockdown for less than an hour Tuesday morning while police responded to the threat. A dispatcher received the call reporting a person in the high school with a gun. The school resource officer immediately responded to that area, and multiple police officers were dispatched to the school to search the building. The school reopened just after 11:12 a.m., according to a news release from the department.

The release said police believe the call was a hoax and did not identify any credible threat at the school, and officers are working to identify the caller.

“The faculty, staff and students did a remarkable job during this incident helping to secure their classrooms and keeping calm,” the release said. “Calls like this are taken seriously until police can be sure the threat is not credible and the students are safe. The school remained in lockdown until that time.”

Police asked anyone with information about the incident to call (207) 874-8575. Anonymous tips can be texted to 274637 (CRIMES) with the keyword “GOTCHA” plus their message, on the department website and on the crime tip line at (207) 874-8584.