LOS ANGELES (AP) – A blackout hit a large portion of the Los Angeles area yesterday afternoon, snarling traffic at intersections and trapping people in elevators.

The city was investigating the cause of the outage. But Sgt Catherine Plows, a police spokeswoman, said terrorism was not suspected.

The electricity went out shortly before 1 pm (2000 GMT), and outages were reported from downtown to the Pacific Coast and north into the San Fernando Valley, an area encompassing hundreds of thousands of residents and thousands of businesses.

Some Los Angeles neighbourhoods did not lose power at all, and electricity was restored in some areas within an hour.

Los Angeles International Airport lost power, but its emergency generator kicked in promptly and no flights were affected, said Harold Johnson, an airport spokesman. The Medical Center of the University of California, Los Angeles, used backup generators and reported no danger to patients.

Downtown high-rises went dark, fire officials said they received reports of people stuck in elevators, and stoplights went out at intersections across the city. Neighbouring cities, including Burbank and Glendale, also were affected.

The Police Department went on “full tactical alert,” meaning no officers were allowed to leave work when their shifts were over.

The blackout came a day after ABC aired a videotape of a purported al-Qaida member making terrorist threats against Los Angeles and Melbourne, Australia, on the fourth anniversary of the Sept. 11 attacks.

US Homeland Security Department spokesman Russ Knocke said federal authorities were talking to state and local counterparts about the power loss, but “there is no indication of any nexus to terror.”