SAN FRANCISCO — The place that helped make the Internet the center of our lives may have to live offline, at least temporarily.

Nearly a million Northern Californians are enduring or preparing for unprecedented blackouts — and top U.S. mobile providers are scrambling to maintain service. AT&T, Sprint and T-Mobile said the shutdowns could interrupt service and make it difficult or impossible to make calls, send texts or access the Internet.

Only Verizon expressed unwavering confidence about its service in the face of the blackouts.

One of the largest utilities in the nation, Pacific Gas & Electric, began shutting off power Wednesday ahead of dry, windy conditions that increase the risk of dangerous wildfires. The blackout affected about 500,000 customers early Wednesday, with additional blackouts expected to affect about 300,000 others on Wednesday and Thursday.

PG&E told customers that power could be out for as long as five days, depending on weather and how long it takes to get power systems back up and running. Some people had lost cell coverage as of Wednesday evening, according to AT&T spokesman Jim Greer. T-Mobile also reported some outages.

All the companies are encouraging customers to fully charge their devices before a scheduled outage, consider purchasing a charging device that doesn't need to be plugged in, prepare an emergency kit and keep in touch with officials for updates.

Backup equipment will be key to whether the connected Bay Area can get online during the blackout.

AT&T's Greer said the company is working as quickly as possible to deploy recovery and generators in areas where customers may be affected. He added, though, that network is performing well despite the outages. AT&T is offering unlimited talk, text and data to its customers in 758 California Zip codes between Thursday and Sunday.

AT&T was informed of the power shutdowns in over 38 counties less than 36 hours in advance, and the information changed in the hours ahead of the blackouts, according to a person close to the situation who spoke on the condition of anonymity.

In a blog post on its website, Sprint said the blackouts could affect cell towers. Some of the sites have generators, and the company says it is deploying backup power as quickly as possible to the ones that don't.

T-Mobile said it has permanent generators in "key cell sites" and backup battery power elsewhere. Temporary generators can also be deployed if necessary.

"We understand that service disruptions are an inconvenience to our customers and we appreciate their patience during this event," T-Mobile said in a statement.

Verizon spokeswoman Jeannine Brew Braggs said the company can serve customers "indefinitely" until commercial power is restored. She attributed that to the generators and backup batteries at the majority of its cell towers and other locations. Brew Braggs said the company can refuel the generators to keep them running.

Officials determined earlier this year that PG&E equipment was responsible for the deadliest wildfire in California history, which killed 85 people, destroyed the town of Paradise and nearby areas and burned 150,000 acres.

PG&E filed for bankruptcy in January in anticipation of $50 billion in liabilities stemming from the disaster.

The San Francisco Chronicle reported that a barricade was set up in front of PG&E's headquarters in the city in to protect employees from frustrated customers.

PG&E did not respond to a request for comment.