PHOENIX -

A United Express flight from San Francisco to San Antonio has been diverted to Phoenix because of a reported threat.

Officials at Phoenix Sky Harbor International Airport say Flight 5573 landed at 4:45 p.m. Thursday.

SkyWest Airlines, which operates flights under the United Express brand, says the 42 passengers, two pilots and two flight attendants aboard the regional jet were evacuated.

The nature of the threat wasn't immediately clear, but airport officials say a Phoenix Police Department bomb squad was called out to search the plane.

They say authorities were searching through luggage after passengers were bused to a waiting area in a terminal.

Sky Harbor officials say the plane has been isolated on the northwest side of airport and the incident isn't causing any flight delays.

This image shows the flight's interrupted route: