Traffic lights, businesses and ATMs were plunged into lunchtime darkness when utility workers accidentally sliced several power lines, startling some in a city already jittery following a purported Al Qaeda threat.

The mishap, which lasted about 2½ hours Monday, cut power to 750,000 homes and businesses — or about 2 million people — from downtown Los Angeles to Venice Beach (search) to much of the city's San Fernando Valley (search).

Inside one downtown high-rise, Albert Vasquez had to pry his way out of an elevator that shut down after the power failed.

"It was bizarre," said Vasquez, 27. "It went completely dark."

As word spread that terrorists were not involved, people calmed down and many, unable to take elevators back to their offices, enjoyed an extended lunch hour on a sunny, pleasant afternoon.

"I'm just reading the paper and seeing a lot of my colleagues out here, so I guess we all have a good excuse," said Ludwig Welsh, who was grabbing lunch outside his downtown insurance office when the power failed.

The outage came just a day after the release of a videotape in which a reported Al Qaeda member said Los Angeles was being targeted for attack. The police department ordered all officers to stay on their shifts and surveyed the city by helicopter.

"We were all freaked out, no doubt," said downtown high-rise worker Vicki Brakl, "especially because this morning there was that video of Al Qaeda."

Hospitals, which also lost power, had to resort to emergency generators. Children's Hospital of Los Angeles (search) suspended all unneeded surgeries for the day.

Gas station pumps also stopped working, car washes came to a halt, assembly lines stalled and restaurant machinery quit in the middle of lunch hour.

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 evacuating.

Electricity-powered devices began shutting down at 12:37 p.m. Power began coming back about 90 minutes later, but electricity wasn't fully restored until 3 p.m., said Gale Harris, a spokeswoman for the Los Angeles Department of Water and Power (search).

There were few reports of injuries or damage, although two men were briefly hospitalized after inhaling toxic fumes at an oil refinery where smoke backed up when employees had to burn off excess chemicals after the power went off.

The smoke created by the burn-off at refineries near the Port of Los Angeles also prompted officials to evacuate Los Angeles Harbor College (search), where students were sent home for the day. People living near the harbor were advised to stay inside and keep their doors and windows closed.

The outage began when workers installing an automated alert system cut several wires simultaneously, instead of one at a time, according to Ed Miller, of the Department of Water and Power.

The error prompted two generating stations and other receiving stations to shut down. That in turn forced the department to begin cutting power to people across the city to stabilize lines.

Though some power experts said the system performed correctly given the surge, it was the latest indication of the vulnerability of the nation's electrical grid.

In 2001, power shortages in the state caused rolling blackouts. And a blackout in August 2003 that started in Ohio cascaded across the East and into Canada, affecting 50 million people.

The latest outage spread north into the San Fernando Valley and hit neighboring cities, including Burbank and Glendale. But because of the region's patchwork utility system, pockets of power remained.

The electricity continued to flow in the seaside city of Santa Monica, for example, while the adjacent Venice Beach section of Los Angeles went dark.

There was confusion at major traffic intersections as motorists tried to nose their cars through darkened stoplights, jamming exit ramps and freeways.

Katie Cerio, a stylist for TV commercials, said traffic signals were out in her Los Angeles neighborhood but they were on in the nearby city of West Hollywood.

"They've got people directing traffic, but it's definitely a bit chaotic," Cerio said from her car.

At the Bob's Big Boy restaurant in Burbank, power was out for about 90 minutes.

"All we could serve were salads and cold sandwiches, no hamburgers," manager Frank Rodriguez said.