Authorities were investigating extensive power outages in southern California, Arizona and Mexico on Thursday that left more than 1 million customers without power, caused traffic jams and prompted at least one county to activate its emergency operations center.

San Diego Gas and Electric said the problem appeared to have originated in Arizona. At least 1.4 million customers were without power, the utility said.

“This caused our line from AZ and from the north of our region to both trip off,” the utility posted on its Twitter account.

“Think of the system as linked by springs, when one part goes out the rest are affected,” another Twitter post from the utility said.

Power outages in California stretched from San Clemente to the state’s border with Mexico on Thursday, a San Diego County spokesman told CNN.

In Arizona, about 56,000 customers in Yuma, lost power, Arizona Power and Supply said.

Parts of Mexico’s Baja California state were also without power, the Civil Protection Department there said, adding that authorities there were working to fix a problem at a hydroelectric plant.

San Diego County had activated its emergency operations center as officials tried to learn more about the blackout, county spokesman Michael Workman said.

“This is crazy, gridlock everywhere,” Brian Korhummel told CNN’s iReport.

CNN affiliate KGTV reported widespread power outages throughout the San Diego area.

San Diego Gas and Electric crews were trying to determine the cause of the outage, KGTV said.

Power went out about 3:45 p.m. in San Diego, said Joe Pettigrew, who said he was trapped on the 10th floor of a high-rise office building.

“We don’t have air-conditioning and the windows don’t open,” he said, noting that it was about 80 degrees outside.

Rebecca Bloomfield of the San Diego airport authority said the airport was only letting inbound flights land. Outbound flights and security screening were halted due to the power outage.

CNN’s Greg Morrison and Tina Burnside contributed to this report.