CONCORD, N.H. – Police officers evacuated Concord High School Tuesday night for a report of a student with a gun, the intense lockdown ending with the arrest of an 18-year-old student for alleged criminal threatening with a dangerous weapon.

UPDATE: Police allege teenage girl "lied" about threat charge UPDATE: Police: "This was all a fabrication"

A surreal scene quickly unfolded as SWAT teams descended on the campus and there were reports of students with blood on their faces – possibly for a zombie play or movie. Among students at the high school at the time, there were some students, dressed in full costume and make-up, filming a movie for an upcoming film festival, according to Principal Gene Connolly. Concord Police Lt. John Thomas said no injuries were reported and the incident is still under investigation.

The building was thoroughly searched and school classes resume as usual May 1, Connolly said in a statement on the school's website. Police were called to the scene at little past 7:35 p.m. for a report of a student allegedly threatening another student with a gun. They quickly cordoned all the streets around the school with yellow tape and police cruisers, which were stretched to a block and half southeast of the school, from Warren Street to the school's off-street parking lot, near North Washington Street.

A SWAT team was called in as well as the New Hampshire State Police, Bow and Dunbarton police departments, with a small command center set up in the school's off-site parking lot. The Concord Fire Department had a rescue team stationed at Memorial Field, just off the school site, to assist if needed.

According to officers speaking over the police scanner, the building was put on lockdown around 8:30 p.m. Officers entered the building and quickly evacuated students participating in afterschool activities and students who were rehearsing as zombies for a play or movie. A number of officers parked on Liberty Street and approached and searched the areas between Liberty and Warren streets.

Police did not comment immediately about the situation. Chief John Duval simply stated that there was a "very serious" incident underway. Other officers reported over the scanner that they were looking to talk to school officials about a potential suspect who was a student at the school. At a few minutes before 9 p.m., officers reported that a suspect was in custody. School Superintendent Chris Rath and Principal Connolly toured the school with police not long after that.