SAN FRANCISCO (AP) — Pacific Gas & Electric says it failed to notify 23,000 customers, including 500 with medical conditions, before shutting off their power to prevent wildfires earlier this month.

In a report filed with regulators Monday, California’s largest utility didn’t say where the affected customers live or if there were any reported medical complications.

PG&E says some customers had no contact information on file. Others were incorrectly thought to be getting electricity from power lines that weren’t turned off.

The outages Oct. 9-12 affected 636,000 homes, 81,000 businesses and 11,000 other customers in the first of a series of mass outages to prevent wildfires caused by electrical equipment.

Millions faced blackouts this weekend while fires are raging on both ends of California, and more shutoffs are expected in the coming days.

PG&E didn’t immediately respond to a request for comment Monday.