Potomac High School in Oxon Hill, Md., was locked down amid confusion following a report of shots fired in the neighborhood.
The person who called authorities reported seeing two people heading toward the school in the 1400 block of Southview Drive about 9:15 a.m., Prince George's County police said.
"They just told us we were on lockdown and it wasn't a drill this time," student said Faith Crudub said.
Teachers and students did not know why the school was locked down.
"In order not to convey erroneous information that may impact safety, very little detail is given about why a school is in lockdown mode," Prince George's County Public Schools Acting Communications Director Max A. Pugh Jr. said in a statement. During a lockdown, as is sometimes the case, erroneous information may be spread through social media."
After the school locked down, a student in the building texted a family member that there may be a gunman in the school, prompting the family member to call police and report a gunman in the school and students in danger, police said.
Police entered to look for the alleged gunman and narrowed their search to two classrooms, where officers patted down students to check for weapons. None was found, police said.
Officers confirmed the report of the gunman in the school was wrong, police said, but they have not been able to confirm the report of shots fire or the two people running toward the school.
The lockdown was lifted before 11 a.m.
"We’ve had lockdowns before but they were never this long," student Semaja Evans said.
Prince George's County police said their extreme response to the reports was due to the extreme nature of the calls: A shooting near a school and a gunman in a school.