A cascade of power failures hit Santa Rosa Memorial Hospital and the surrounding neighborhood Thursday, darkening traffic lights, offices, homes and Montgomery Village shops in waves throughout the day.

Two trauma patients -- a stabbing victim and a pedestrian struck by a van -- were flown to out-of county hospitals late Thursday as the enduring equipment problems forced Memorial Hospital to operate on generator power. A third trauma patient was taken to Sutter Hospital in Santa Rosa.

"We are on backup power, and as a precaution we would not undertake serious surgery under those circumstances," hospital spokeswoman Katy Hillenmeyer said.

An underground equipment failure caused the first of three failures at 9:30 a.m., cutting power for 1,025 customers in the Montgomery Village neighborhood, PG&E spokeswoman Brittany McKannay said.

"A piece of equipment called an elbow failed," she said.

As power was being restored, the underground equipment on Sonoma Avenue near Doyle Park experienced additional problems, cutting power again.

The 4:15 p.m. failure left about 1,100 customers in the dark, McKannay said.

Crews began restoring power by diverting customers to other circuits. But the system became overloaded, spokesman JD Guidi said. About 1,100 customers lost power at 6:47 p.m.

"As they re-routed power, the load was too large," Guidi said.

Late Thursday, Guidi said he did not know when power would be restored.

During the outages, the generators for the Montgomery Drive hospital kicked in automatically and the county's trauma center didn't lose power, Hillenmeyer said.

But without a backup to the emergency generators, she said trauma patients would continue to be diverted elsewhere.

You can reach Staff Writer Julie Johnson at 521-5220, julie.johnson@pressdemocrat.com or on Twitter @jjpressdem.