A new voting system in Los Angeles County faced its first big test on Super Tuesday, the culmination of a decade of work on what was envisioned as a model for the nation. But technical glitches caused hours-long lines across the county — the largest in the country with more than 5 million registered voters — and harsh criticism from candidates, voters and political parties.

About one-fifth of the county’s touch-screen voting machines did not work properly and had to be replaced, county spokesman Michael Sanchez said late Tuesday, for reasons he said he could not specify. He also said that network problems in multiple locations interfered with electronic poll books used to verify voter eligibility, forcing some voters to cast provisional ballots. Those will take longer to count.

“We believed in the technology and we believed it would work, because that’s what we were told,” said Mark Gonzalez, chair of the county’s Democratic Party. “And that’s not what happened. Machines completely went out. ­Voting centers completely shut down.”

Janice Hahn, a member of the county’s nonpartisan board of supervisors, said she plans to press for the county registrar’s office to investigate the failures and explain within 30 days how they can be remedied before November’s general election.

“It was $300 million and a period of years that we have been developing this, so it was very troubling that on the day of the actual vote there were some big problems,” Hahn said. “The reason we changed to this system was to create more access for people and more flexibility, so I want to make sure that the problems people experienced yesterday didn’t cause just the opposite of what we were attempting to do.”

Los Angeles County has worked for years to develop its own voting system, one that was to be accessible to voters with disabilities and non-English speakers. As the first publicly owned voting system in the United States, it would also ease the grip that a handful of private companies have long held on how Americans vote, supporters of the effort said.

The system’s custom-made voting machines feature oversized buttons and can be adjusted for people in wheelchairs. Voters can choose from 13 languages and listen through earphones if they have impaired vision or prefer audio. The machines — called ­ballot-marking devices — print out a paper record that voters can verify and then feed into a ballot box.

Dean Logan, the Los Angeles County registrar of voters who led the development of the system, did not respond to calls seeking comment Wednesday. On Tuesday, he told the Los Angeles Times: “This was a challenging day for a lot of voters in L.A. County and I certainly apologize for that.”

The widespread reports of difficulties prompted the campaign of Sen. Bernie Sanders (I-Vt.) to ask a federal judge to extend voting in the county by two hours, requiring that polling places remain open for anyone in line by 10 p.m. In its filing, the campaign wrote that significant problems — including wait times of up to four hours — were reported at more than a dozen polling locations.

Court records do not show a response from the judge, and the voting hours were not extended.

“Voters should never have to wait four hours in line to exercise their constitutional right to cast their ballot,” said Anna Bahr, a Sanders campaign spokeswoman. “Long wait times and malfunctioning machines like the ones we saw yesterday disproportionately affect working-class voters who can’t afford to take extra hours off work or pay for child care to stand in line.”

Voter advocates, election observers and candidates expressed frustration that the county was using a new system for the first time during such a crucial election.

Before Super Tuesday, Logan told The Washington Post that the system had functioned well during a mock election last fall and that “feedback from those voters was very positive.”

For voters, the changes were not limited to new technology. Los Angeles residents previously voted at their neighborhood precincts. In the new system, voters can cast their ballot anywhere in the county, but the number of polling locations dropped from more than 4,000 to fewer than 1,000.

On Tuesday, Gonzalez, the county Democratic chair, said he saw elderly voters and those with disabilities waiting in line for hours, despite the county’s ambitions for a system that would work best for the most vulnerable.

At the University of California at Los Angeles’s Ackerman Student Center, students and staff reported waiting in line for up to two hours. Some simply left, saying they could not miss work or class. Volunteers held up whiteboards showing other voting locations nearby.

A county poll worker, who spoke on the condition of anonymity because he had been instructed not to talk to the press, said the Internet connection on campus was too slow to support the poll books. Provisional ballots were being handed out instead.

At the same time, many said they were able to use the voting machines effectively. “If you live on a smartphone, it’s not difficult to use this system,” said voter Valarie Kaur, 39.

While technical glitches were reported elsewhere in California, Los Angeles County’s problems were widely felt in part because of its reliance on voting machines. Many other counties send mail-in ballots automatically to every registered voter and offer mostly hand-marked paper-ballot options at polling places. Los Angeles County sends mail-in ballots only to those who request them or who have voted by mail previously and expects most voters at polling locations to use the machines.

The county’s website showed that as of Wednesday morning, with the counting still underway, about 651,000 voters had cast ballots on the new machines and about 486,000 had voted by mail. It is not clear how many voters had to cast provisional ballots.

Advocates, local candidates and political party staffers criticized county officials and California Secretary of State Alex Padilla for not doing more to anticipate such problems, especially following the spectacular failure of a mobile app used in Iowa’s first-in-the-nation caucuses.

A December report commissioned by Padilla’s office said the system did not meet several of the state’s cybersecurity and accessibility standards. Those standards were to be “woven directly into the DNA” of the new system, according to the county’s contract with Smartmatic, the private company that built the voting machines.

The report said several standards had not been met: The machines that tally the results could be started by inserting a flash drive, creating an opportunity to infect them with malware, and the system lacked a security measure known as “full disk encryption,” a cybersecurity gold standard. Padilla in January certified the system for use in the March primaries anyway, imposing certain conditions such as placing tamper-evident seals and protective covers on some of the equipment.

His office also ordered the county to address the ballot misfeed rate cited in the report, which found that the rate — essentially, of paper jams — was five times higher than the state standard. It’s not clear if that issue was addressed during the primaries, though many voters reported that issues with paper jams contributed to long lines Tuesday.

Padilla’s office did not respond to requests for comment Wednesday.

Smartmatic’s chief executive, Antonio Mugica, congratulated the county on Twitter on Wednesday, writing: “Long lines in some centers, sure. Areas of improvement, absolutely. — But I don’t know anyone that could have pulled this off on the first try!”

Stanley-Becker reported from Los Angeles. Alice Crites in Washington contributed to this report.