Multiple floors and corridors inside the Pentagon were locked down and partially evacuated Thursday after building systems detected what officials described as a hazardous materials incident, according to sources and the Arlington County Fire Department.

Pentagon spokesman Sean Parnell confirmed the situation, telling Axios that systems within the building “have detected an air quality issue necessitating precautionary measures until we determine its significance.” A shelter-in-place order was issued for the affected area, Mr. Parnell said, and response teams were deployed to support building occupants.

Floors two through five in corridors four through seven of the sprawling Pentagon complex were locked down, two sources said. A third source told CNN that police inside the building were wearing gas masks and full chemical protective gear.

An internal security message obtained by CNN said additional testing of the air quality issue could take one to two hours and warned occupants they might observe “response personnel from multiple agencies and precautionary measures taking place in the center courtyard.”

The Pentagon Force Protection Agency’s hazardous materials team responded to the incident alongside the Arlington County Fire Department, according to department spokesperson Capt. Jamie Jill. Arlington Fire & EMS posted on social media that its hazardous materials team was “operating at the Pentagon in support of PFPA’s Hazmat Team during a hazardous materials incident.”