SACRAMENTO, Calif. (AP) — Californians are voting in record numbers, with more than a third of the state's 22.3 million ballots already returned to county election offices one week before Election Day.

Yet at the Oak Park Community Center in Sacramento on Sunday, it was so slow that poll worker Tom Martinez had to get up and move every so often to keep the motion-detected lights from going out.

While counties nationwide are reporting hours-long wait times to vote early, voters in the nation's most populous state are putting their ballots in the mail after a state law passed this year required county elections offices to send ballots to all active registered voters at least 29 days before Election Day.

Most of the state's in-person polling places — or vote centers — won't open until Saturday. The state allowed counties to open fewer of them this year because the coronavirus pandemic has made traditional polling places unavailable, like schools and senior centers. Ventura County had 389 polling places in March but will have just 48 vote centers this weekend.

Most Californians already vote by mail. Nearly 58% of ballots cast in the 2016 presidential election were by mail, which rose to 72% in March's primary. Even if that 72% holds this November, that still leaves millions who could vote in person at vote centers that must maintain physical distancing and take time to clean equipment between each voter.

“I guarantee you there is going to be lines around the block in many polling places and in many areas where voters haven't been used to seeing lines," said Paul Mitchell, vice president of Political Data Inc., a bipartisan voter data company based in California.

Is the unprecedented return of mail-in ballots a sign that fewer people will vote in-person this year? Or are those voters people who would vote anyway and just a preview of the crush of people expected on Election Day?

State officials hope it isn't the latter. Some vote centers opened in a few counties on Saturday, offering a preview of what voting in person during a pandemic will look like. The NBA's Sacramento Kings donated its cavernous arena as a vote center, allowing people to cast ballots with a view of the court beneath a Jumbotron. It has about 42 voting booths compared to polling places in recent years that had about six. But at lunchtime Monday, the center was mostly deserted. About 178 people voted there over the weekend.

Secretary of State Alex Padilla, the state's chief elections officer, doesn't think that trend will last.

“Given the anticipated big voter turnout, along with physical distancing and safety measures at in-person voting locations, there will likely be longer lines and wait times on Election Day," Padilla said in a news release. “Californians should not wait — they should vote early.”

Republicans have historically been more likely to vote by mail in California. This year, though, Republican President Donald Trump has criticized vote-by-mail because he says it is ripe for fraud. Mitchell said polls show about 44% of Republican voters said they plan to vote on Election Day while 57% of Democratic voters said they would vote early. Padilla has said there is no evidence of fraud and voters should feel confident mailing their ballots.

Republicans have been trying to boost turnout by placing some unofficial ballot drop boxes in counties with closely contested U.S. House races. At first, state officials said the boxes were illegal. They've since backed off that somewhat, although Democratic Attorney General Xavier Becerra is still investigating them.

Los Angeles County opened 118 vote centers on Saturday, with nearly 50,000 people casting ballots in person. There were no long lines, according to Mike Sanchez, spokesman for the Los Angeles Registrar's Office. That's up from the roughly 10,000 people who cast ballots in Los Angeles County during the first weekend of in-person voting for the March 3 primary. But it's just a fraction of the more than 1.6 million vote-by-mail ballots the county has already received.

An additional 649 vote centers will open in LA County on Saturday, including the Museum of Latin American Art in Long Beach, which is using a 7,000-square-foot meeting room for a vote center, with a roll-up door open to improve airflow. When it opens Saturday for four days of voting, it will be the first time people have been inside the building since mid-March.

Long Beach is about 42% Latino, and the museum is preparing for a big turnout. Museum officials said people have already been calling to ask when they can vote.

“We're hopeful it will be big crowds," said Todd Heustess, the museum's vice president of development. “We want as many people voting as possible.”

Smaller counties have fewer options. In Butte County, which has been devastated by wildfires in recent years, officials are using the local Elks Lodge for the first time after the state Legislature changed the law to allow people to cast ballots near places that serve alcohol.

“We don't have any what I call “sexy places" like Dodger Stadium in our county, but we have a lot of good people voting,” Butte County Registrar Candace Grubbs said.

At the Oak Park Community Center in Sacramento, poll worker Paul Bergman keeps a spray bottle handy filled with a 70/30 solution of isopropyl alcohol to wipe down booths after each voter. They don't let voters use the bathroom because they don't want to have to do the same thing in there each time it's used.

Bergman hasn't had much to do yet as turnout has been light. But outside, where a pink drop box sits for voters to place ballots they filled out at home, Sukhdev Rye has been busy. The poll worker estimated more than 100 people came by Saturday to drop off their completed ballot.

“People wanted to vote," he said. “This is the most gratifying voting experience that I've been a part of."

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Associated Press videographer Haven Daley contributed from San Francisco.