Hundreds of thousands of residents of El Paso, Texas, Las Cruces, New Mexico, and surrounding areas lost power early Friday when three high voltage transmission lines failed, a utility spokesman said.

The outage was caused when three 345-kilovolt lines owned by El Paso Electric Co. tripped off, leaving area residents without electricity in upwards of a half hour, company spokesman Henry Quintana told Reuters.

"Everybody in our service territory was out," Quintana said, referring to the company's 340,000 customers in the Rio Grande Valley in West Texas and southern New Mexico.

Local media reported that traffic light outages were the biggest problem.

Most television and radio stations were knocked off the air and flights at El Paso International Airport were delayed while officials worked to get back-up generators on line.

The city of El Paso lost power at about 9:45 a.m. Mountain time, with some customers having power restored 30 minutes later. Quintana said about a quarter of their customers were still without power this afternoon.

"We lost all three of our transmission lines at the same time. The lines came back on at 10:15, a half hour later, but we still have parts of the city that are out ... we have to bring them up slowly so that we don't damage the distribution system," Quintana said.

The lines run from Albuquerque, New Mexico to El Paso with two lines running west toward Phoenix, Arizona, Quintana said.

There were reports of outages in other areas not served by El Paso due to the fact that other local utilities receive power from those transmission lines, Quintana said.

He said they did not know what caused the lines to fail.

"It may be a while before we even find out what happened because those transmission lines stretch over thousands of miles of land," Quintana said.

In neighboring New Mexico, customers of Public Service Company of New Mexico (PNM), a unit of PNM Resources , had voltage fluctuations as El Paso was trying to bring their system back on line.

"People here saw their lights flicker and their computers flicker, but we didn't have any outages as a result of their problem," PNM spokesman Don Brown said.

PNM serves about 350,000 customers in New Mexico, Brown said.