Authorities say 30 Tennessee counties have received false bomb threats to courthouses or other government buildings.
The threats began Tuesday morning and forced evacuations while authorities searched for bombs.
Tennessee Department of Safety and Homeland Security spokeswoman Dalya Qualls said no explosives were found and no arrests have been made.
A spokesman for the Tennessee Emergency Management Agency said the threats were made in phone calls to county clerk offices.
In Memphis, police said an unknown woman called and said she had information that someone was going to blow up three buildings in the city, including the federal building and a post office.
Tennessee became the fourth state this month to deal with widespread bomb hoaxes. Oregon, Nebraska and Washington all had similar threats reported to courthouses.