Police sound "all clear" after bomb threat at Facebook's Silicon Valley campus

FILE PHOTO: The entrance sign to Facebook headquarters is seen in Menlo Park, California, on Wednesday, October 10, 2018. REUTERS/Elijah Nouvelage/File Photo

SAN FRANCISCO (Reuters) - A bomb threat prompted authorities on Tuesday to evacuate a building at the Silicon Valley headquarters of Facebook Inc , police said, but gave the "all clear" after an hours-long search turned up no sign of a device.

The New York Police Department had received an anonymous tip about a bomb threat regarding Facebook's campus in Menlo Park, California, and alerted local authorities at about 4:30 p.m., a spokeswoman for the Menlo Park police said.