(CNN) Two California utilities said they may cut power to more than 900,000 customers for days starting after midnight Wednesday morning because of dry winds that could down power lines and cause fires.

San Jose Mayor Sam Liccardo on Monday urged residents and businesses to prepare to be without electricity for as much as a week, saying the outages could affect almost 2 million people

Pacific Gas & Electric and Southern California Edison on Tuesday raised the number of its customers who may be without power from 600,000 to almost 800,000, affecting 34 northern, central and coastal counties, starting with counties in the north just after midnight Wednesday morning.

Southern California Edison said it's considering cutting power to more than 100,000 customers in eight counties. The utilities haven't said how many people the outages will affect in all.

A map from PG&E shows the areas where power may be cut.

"Given the prolonged period during which the wind event will unfold, and the large number of power line miles that will need to be inspected before restoration, customers are being asked to prepare for an extended outage," PG&E said in a release.