A "serious software error" at New Jersey's Department of Motor Vehicles led to around 6,600 non-US citizens being registered to vote, with "fewer than 400" of them wrongly casting ballots, the state's governor said.

"I am appalled by the reckless failures that allowed this to happen," Governor Mikie Sherrill said in a statement on Tuesday.

The disclosure comes as the Trump administration is pushing to pass strict new voter-ID and proof-of-citizenship rules in Congress.

The residents, who were registered to vote between June 2023 and June 2024, had indicated that they were not citizens. "But through no fault of their own, the system registered them anyway," the governor said.

Governor Sherrill said the accident happened when residents applying for drivers' licenses and identification cards answered 'no' on a keypad when asked whether they were a US citizen.

"Our preliminary analysis shows fewer than 400 individuals who were newly registered for the first time because of the error voted," she said.

The governor added that the group included people registered as Democrats, Republicans and Unaffiliated voters and that they were scattered around different parts of the state. The error took place before she took office, Sherrill said.

Sherrill said the vendor responsible for administering the ID system would be replaced.

President Donald Trump has long advanced unsubstantiated claims of widespread voter fraud in US elections. He has recently pushed for Congress to pass the SAVE America Act, which would create nationwide rules for voting, which is administered by states.

Sherrill, a Democrat, said in her statement that "Trump has zero credibility on the issue of election integrity", and that he has spread "lies" about US voting systems and attempted to overturn his 2020 election loss to Joe Biden.

She vowed to address the issue, contrasting her administration's approach to Trump's.

"The difference is simple: when we find a problem, we don't hide it, deny it, or invent conspiracies. We investigate it, we fix it, and we tell the public," Sherrill said.

Republicans quickly seized on the news to advocate for the passage of the SAVE Act.

"Yet another reason to PASS THE SAVE AMERICA ACT!" the White House's rapid response team wrote on X.

Congresswoman Laurel Lee, a Florida Republican, called the error a "catastrophic failure" and called for an investigation.

Last week, Department of Homeland Security Secretary Markwayne Mullin told states their voter rolls "needed to be scrubbed" of ineligible voters.

He warned that the Trump administration could potentially withhold federal election funds to states that did not comply.

DHS has urged states to use their newly expanded national database to check whether noncitizens had registered to vote. But investigations by ProPublica and ABC News have found the system had the potential to incorrectly flag US citizens who are eligible to vote.

The Trump administration has been locked in legal battles with several states over their election administration and voter rolls.

In the US, individual states administer elections, not the federal government. But the Trump administration has attempted to exert more federal control over the election process heading into November's midterm elections.