Police responded shortly before 10:30 a.m. to report a person walking away from the black briefcase, which appeared suspicious, near the Diamond Head Inn at 605 Diamond St., San Diego police Officer Frank Cali said.
Police later contacted fire personnel, and the Metro Arson Strike Team was summoned, the officer said. As of early afternoon, the investigators remained on scene, a San Diego Fire-Rescue Department dispatcher said.
No injuries were reported, Cali said.
Those in the immediate area were evacuated as a precaution, Cali said.
Diamond Street was blocked off between Mission and Ocean boulevards, Cali said.