An electrical power outage has affected the cities of Bisbee and Douglas tonight.

An open breaker on a transformer caused 13,500 customers to lose electricity in both cities beginning at 7:39 p.m. Thursday, said Damon Gross, an Arizona Public Service spokesman based in Phoenix.

By 8:30 p.m., a total of about 6,000 customers remained without power in both Douglas and Bisbee, Gross said.

Terrie Kjos, a resident of Old Bisbee, said her outdoor thermometer read 36 degrees at 9 p.m. The community still had snow on the ground from snowfall earlier in the week, she said.

“There are some people who only have space heaters,” Kjos said. “We have a gas heater in our bedroom, but the electric heaters in the rest of the house are out.”

“Most people in the neighborhood are staying indoors,” Kjos said. “The longer the outage, the colder it will get for people inside their homes,” she said.

The cause of the breaker malfunction was not known, Gross said.

He said crews were expected to work through the night to restore power to all customers.