SONOMA, Calif.  — California’s biggest utility cut power to more than a million people Wednesday for what could be days on end in the most sweeping effort in state history to prevent wildfires caused by windblown power lines.

The unpopular move sparked a run on supplies at stores and came after two years of catastrophic fires sent Pacific Gas & Electric into bankruptcy and forced it to take more aggressive steps to prevent blazes.

The drastic measure caused a wave of impacts, from long lines at supermarkets and hardware stores to backups at traffic lights that had gone dark. Schools and universities canceled classes, offices were closed and many businesses were shuttered.

With the sun shining, not a wisp of smoke in the air and only gentle breezes, the historic action was condemned by those inconvenienced.

“It’s unreasonable. There’s no wind. It’s nothing. There’s no reason why they should shut the power off,” said Joseph Pokorski, a retiree who had been drinking beers and cocktails by lantern light at the Town Square bar in Sonoma in the early morning. “They’re … closing everything down so they don’t get sued. They don’t trim the trees, so we suffer.”

More than 500,000 customers in Northern California were without power, the utility said, and about 300,000 more outages were planned later to prevent its equipment from sparking wildfires during winds forecast to build. About 2 million people were expected to be affected for up to several days.

“To everyone asking, ‘Where’s the wind? Where’s the wind?’ Don’t worry, the wind is coming. Go for a hike above 4,000 feet and you’ll feel it,” said Steve Anderson, a meteorologist with the National Weather Service’s Bay Area office. “Obviously PG&E doesn’t want to cut the power when there’s already strong winds. You want to cut the power before it happens.”

Before the lights went out in the East Bay town of Moraga, cars were lined up at gas stations and customers filled carts at the town’s only supermarket with bags of ice, canned goods, loaves of bread, breakfast cereal and water.

Lines were also long at pharmacies and hardware stores, where emergency supplies were running low.

“Do you have any lanterns?” a concerned Elma Lear asked at Moraga Hardware and Lumber. “Or candles?”

The store was out of both and had also run out of batteries and coolers — even ultra-pricey Yeti coolers that cost as much as $400, owner Bill Snider said.

On Tuesday, the store sold 500 flashlights. Other high-demand items were extension cords, propane tanks for barbecues and butane for camping stoves. Generators were almost impossible to find.

Lear, who had stocked up on nonperishable food, cash and filled her gas tank, was directed to a home decor shop nearby where she had to fork over $40 for long lasting beeswax candles.