Authorities said they're looking through the cargo of a San Francisco-bound flight from Manila after a telephone threat was made to a Philippine Airlines office.
Police Sgt Michael Rodriguez said the plane was taken to a remote part of San Francisco International Airport when it landed on Tuesday night.
He said authorities have not found anything suspicious but that the search is ongoing.
He said the threat made to an airline cargo office was "unsubstantiated" and did not release any details of the threat or whether it had targeted a specific flight.
The airline's website showed it was the only San Francisco-bound flight from Manila on Tuesday.
He said the 337 passengers and 20 crewmembers were taken off the plane as authorities inspected the cargo.