Utility workers connected the wrong wires and caused a blackout across major portions of Los Angeles on Monday afternoon, trapping people in elevators and snarling traffic at intersections, authorities said.
Hundreds of thousands of people were affected by the resulting power surge and outages, which were reported from downtown west to the Pacific Coast and north into the San Fernando Valley.
Several workers who were installing an automated transmission system hooked up the wrong wires, according to Ron Deaton, general manager of the Los Angeles Department of Water and Power.
"They connected it to another line that was not expecting that much electricity," he said. No injuries were reported.
CBS Station KCBS-TV reports that power has been restored to 90 percent of customers, according to the Los Angeles Department of Water and Power.
Deaton said he expected all power to be restored by 5 p.m. local time.
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. Neighboring 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.
But calm prevailed in downtown Los Angeles around midday. Office workers took the opportunity for an extended lunch as police and fire sirens echoed in the background.
The blackout came a day after ABC aired a videotape of a purported al Qaeda member making terrorist threats against Los Angeles and Melbourne, Australia, on the fourth anniversary of the Sept. 11 attacks.
But even before the utility explained what happened, Homeland Security Department spokesman Russ Knocke said said there was no indication of terrorism.
Some Los Angeles neighborhoods did not lose power at all.
Los Angeles International Airport lost power, but its emergency generator kicked in promptly and no flights were affected, said Harold Johnson, an airport spokesman. UCLA Medical Center used backup generators and reported no danger to patients.
Los Angeles operates its own power utility, which serves 1.4 million electricity customers. Customers of Southern California Edison, the largest utility in Southern California, were not affected, according to spokesman Gil Alexander.
Katie Cerio, a stylist for TV commercials, said traffic lights were out in the Torrance neighborhood.
"They've got people directing traffic, but it's definitely a bit chaotic," Cerio said as she drove. "But now I just entered West Hollywood and the traffic lights seems to be on."
At the downtown YMCA, staff used flashlights to help usher exercisers from the pool and other areas to locker rooms so they could dress before leaving.