The Hayward Hall of Justice was evacuated for about an hour Tuesday morning due to a bomb threat, police said.

An anonymous call from a pay phone at 9:37 a.m. claimed a bomb was in the building at 24405 Amador St., said Hayward Police Sgt. Eric Krimm.

Authorities evacuated the building just after 9:40 a.m. About 400 people waited across the street as Hayward police officers and Alameda County Sheriff's deputies searched the building.

About two dozen deputies and officers searched the building and did not find anything, according to Alameda County Sheriff's Sgt. J.D. Nelson.

At 10:33 a.m., a deputy used a loudspeaker to advise the evacuees that they could cross the street and re-enter the building.

Alan Herren, of Castro Valley, was serving on a jury in a criminal case when the bailiff addressed the courtroom, telling everyone they needed to leave. The bailiff didn't give a reason for the evacuation, Herren added.

"They didn't tell us anything," he said. "(There was) no information."

Still, people inside the courthouse evacuated in an orderly fashion, Herren said.

Check back for updates.

Contact Natalie Neysa Alund at 510-293-2469. Follow her at Twitter.com/nataliealund.