The agency, along with New Hampshire State Police, the fire marshal's office, and other federal, state and local agencies went to the building at about 8 a.m. in response to "an unattended item with an unknown substance that warranted a hazmat response in an abundance of caution," Kristen Setera of the FBI said in a statement.

MASSACHUSETTS HIGH SCHOOL STUDENTS EVALUATED BY HAZMAT TEAM AFTER EXPOSURE TO SCIENCE LAB CHEMICALS

She said while the investigation is ongoing, "there is not believed to be any associated threat to public safety at this time."

The Concord School District put out an announcement that courthouse staff and visitors were evacuated to the Christa McAuliffe School gymnasium nearby.