An accidentally severed fiber-optic cable in Virginia effectively shut down most of the state’s online voter registration on its last day Tuesday, prompting voter advocates to file a lawsuit in federal court seeking an extension of the deadline that they argue thousands of voters missed because of the disruption.

Gov. Ralph Northam (D) said most of the state’s Internet service was cut off after the cable in Chesterfield County was inadvertently severed during roadside work related to an ongoing utilities project near Route 10. A spokeswoman with the state’s information technologies agency said it occurred sometime overnight and was discovered early Tuesday.

The disruption, which lasted until about 3:45 p.m. Tuesday, also affected online services provided by the state Department of Motor Vehicles, the Department of Health and several other agencies.

But its deepest impact was felt by the state Department of Elections during what has been a record turnout for early voting in Virginia.

On Tuesday evening, lawyers for a trio of civil rights groups filed a lawsuit in the U.S. District Court in Richmond seeking to have the deadline extended until 11:59 p.m. Thursday.

“A significant number of Virginia residents register to vote in the days leading up to the registration deadline,” said the complaint, which names as defendants the state Department of Elections, the department’s commissioner and members of the state electoral board.

The complaint argues that the cutoff will mostly hurt ethnic minorities and younger voters in the state, who “tend to register disproportionately at higher rates during the last days of the registration period.

Attorney General Mark R. Herring filed a brief supporting the plaintiffs’ complaint late Tuesday. “We need to make up for the time lost today,” Herring said in a tweet. “We have 21 days until the most important election of our lifetimes and I want to make sure every eligible Virginian who wants to vote can.”

With tensions high around the race between President Trump and former vice president Joe Biden, the problem added another headache for local election officials, who spent much of Tuesday fielding complaints from people who were unable to register or who had to wait to have their ballots processed after showing up for early voting.

“It’s terrible because we’re sitting here and we have no idea what’s happening,” Judy Brown, the general registrar in Loudoun County, said while waiting Tuesday morning on state election officials to send word about when the problem would be fixed.

Brown said the connectivity problem forced her office to manually confirm the registration status of Loudoun County voters who cast early ballots Tuesday.

The disruption also prevented Loudoun election officers from processing voter registration applications and from printing labels needed to mail absentee ballots, Brown said.

Officials in Fairfax and Prince William counties said the problem affected only their ability to register voters online. Virginia Beach officials said it hampered their ability to handle early in-person voting.

Christine Lewis, Virginia Beach’s deputy registrar for elections, said voters who showed up to cast their ballots were being offered the option of instead filling out provisional ballots, which are typically counted last in an election.

“It’s affecting everyone,” Lewis said, referring to the multiple state websites that were not operating. “Just because one wire got cut.”

With similar complaints pouring in from other local election officials throughout the state, Northam said he would support extending the voter registration deadline, echoing calls to do so from Lt. Gov. Justin Fairfax (D), former governor Terry McAuliffe (D), several other Democrats and some Virginia Republicans.

But because the deadline is mandated under state law, the move would have to be made through a court order, in the same way it was in 2016 after a state computer system crash caused a similar disruption, Northam said. That year, a federal judge ordered registration to be reopened for an extra two days.

“We have been exploring all of our options to extend the voting registration deadline,” Northam said during a news conference. “That deadline is set in our code, and it does not appear that I have the authority to change it.”

Despite the shared commitment to minimize the impact, the Lawyers’ Committee for Civil Rights Under Law, which is representing the three civil rights groups in the lawsuit, criticized the Northam administration for not doing more to prevent the disruption.

The group sued Virginia for the 2016 deadline extension, which resulted in 36 extra hours of registration time that year.

A figure for how many Virginia voters were actually affected Tuesday was not available, a Department of Elections spokeswoman said Tuesday.

Dave Backus, 49, said he and his wife tried to vote Tuesday at their elections office in Augusta County but were told that the machines were not working.

An elections officer asked whether they wanted to fill out a provisional ballot, but the couple decided to instead return Wednesday, slightly irritated by the inconvenience of having to skip another morning of work.

“We had been planning on this for a good while, and I even called the registrar’s office to check on lines,” Backus said.

Until Tuesday’s disruption, voter registration in Virginia had been robust. At the end of August, there were 5.8 million registered voters in the state, about 300,000 more than in 2016, according to state statistics.

Voter registration for Virginia’s neighbors in Maryland and the District — which also had voter registration deadlines Tuesday — has also been swift.

In D.C., elections officials gathered Tuesday just outside the Entertainment and Sports Arena, serving as the District’s newest voting supercenter, in one final push to get people registered. They were joined by former athletes from local sports teams who stressed the significance of participating in the year’s election process.

The total number of registered voters in the city was 510,400 as of Monday, according to D.C. Board of Elections spokesman Nick Jacobs, up from 496,700 through May 31 of this year and nearly 480,000 in October 2016.

Tuesday was the last day to register online in D.C. in advance of the election, although people can also register in person during early voting, which begins Oct. 27, or on Election Day.

“If you don’t think your vote counts, then you’re sadly mistaken — every vote counts, and the people most affected [by this process] is the young Black community,” said former Washington wide receiver Josh Morgan. “For me, all those people who used to ask for tickets to the game, come vote.”

Simone Stringfellow, 19, was one of several voters to register for the first time at Tuesday’s event, which she attended with her mother. A Ward 6 resident, Stringfellow said she is ready to see new leadership in the White House.

“I don’t like how Trump represents us. I think we need something different,” Stringfellow said. “I’m happy about voting because at least it means I have a say.”

In Maryland, the deadline to register online in advance of Election Day was 9 p.m. Tuesday.

The state offers same-day, in-person voter registration on Election Day and during early voting, which begins Oct. 26.

Over 33,500 voters have joined the rolls in the past six months, according to state data. That has pushed the state’s total to more than 4.1 million people — about 214,000 more than in 2016.

Michael Brice-Saddler and Erin Cox contributed to this report.