Hundreds of Southern California electrical customers had their power cut Wednesday and more than 200,000 others faced the same prospect as utility companies sought to prevent wildfires as Santa Ana winds developed.

Red flag warnings were posted at late morning and were expected to remain in effect through much of Friday due to predicted strong gusts and very low relative humidity, the National Weather Service said.

The strongest and potentially damaging gusts were expected from Wednesday night through Thanksgiving morning. Gusts to 75 mph (121 kph) were expected near and below Cajon Pass and near the coastal foothills of the Santa Ana Mountains.

“Fire danger will rapidly escalate during the night,” forecasters said.

The Santa Anas brought the prospect of public safety power shutoffs in high-risk areas to prevent wildfires from being sparked if the winds were to damage power equipment or blow debris into power lines.

Southern California Edison said power was cut to more than 460 customers in San Bernardino County and shutoffs were possible for more than 150,000 customers in six counties.

San Diego Gas & Electric was considering shutting off electricity to more than 53,000 customers.

Forecasters also warned of a possible overnight hard freeze in the Antelope Valley north of Los Angeles.