A power outage along Sierra Highway spread to nearly 8,000 Edison customers in Newhall and Canyon Country on Sunday afternoon.

The outage  started Sunday at 1:21 p.m. when underground equipment failed near the intersection of Sierra Highway and Via Princessa, Edison spokeswoman Anna Frutos-Sanchez said.

At first the outage was limited to 241 customers, but it quickly spread to nearly 5,000 homes and businesses in the Whispering Leaves and Jake’s Way areas.

By 4:45 p.m. as many as 7,878 customers were affected, despite Edison workers’ efforts to isolate the problem and limit the number of affected customers.

SCV Sheriff’s Lt. Tom Bryski said traffic signals were out Sunday afternoon at the intersections of Sierra Highway and Flying Tiger Drive, and Sierra Highway at Whispering Leaves Drive. SCVNews.com tipsters also reported signal outages on Sierra at the Highway 14 exit, and at Sierra-Princessa where people were reportedly driving through the intersection without stopping.

Tipsters reported outages along the Sierra Highway corridor from Jake’s Way on the north to Placerita Canyon on the south. Costco and the Stater Bros. supermarket remained up and running, they said.

Edison attributed the equipment failure to extreme heat. By 11 p.m. there was still no estimate for when power would be fully restored.

Smaller outages were reported in parts of Valencia throughout the afternoon, each affecting between 39 and 139 homes.