Election campaign posters for French centrist presidential candidate Emmanuel Macron and far-right candidate Marine Le Pen are displayed in front of the polling station where Marine Le Pen will vote in Henin Beaumont, northern France, Saturday, May 6, 2017. Voting for France's next president starts in overseas territories and French embassies abroad, as a blackout on campaigning descends so that voters can reflect on whether to entrust their country's future to independent Emmanuel Macron or far-right populist Marine Le Pen. (AP Photo/Francois Mori)

Election campaign posters for French centrist presidential candidate Emmanuel Macron and far-right candidate Marine Le Pen are displayed in front of the polling station where Marine Le Pen will vote in Henin Beaumont, northern France, Saturday, May 6, 2017. Voting for France's next president starts in overseas territories and French embassies abroad, as a blackout on campaigning descends so that voters can reflect on whether to entrust their country's future to independent Emmanuel Macron or far-right populist Marine Le Pen. (AP Photo/Francois Mori)

PARIS (AP) — France’s election campaign commission said Saturday “a significant amount of data” — and some fake information — has been leaked on social networks following a hacking attack on centrist Emmanuel Macron’s presidential campaign. It urged citizens not to relay the data on social media to protect the integrity of the French vote.

France’s government cybersecurity agency will investigate the attack, according to a government official who said it appeared to be a “very serious” breach.

The leak came 36 hours before the nation votes Sunday in a crucial presidential runoff between Macron and far-right candidate Marine Le Pen — and just as a two-day blackout on campaigning began so that voters could reflect on their choice.

Voting started Saturday in France’s overseas territories and in some embassies abroad.

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The leaked documents appear largely mundane, and the perpetrators remain unknown. It’s unclear whether the document dump will dent Macron’s large polling lead over Le Pen going into the vote.

The election commission met Saturday after the leaks emerged just before midnight Friday. The commission said the leaked data apparently came from Macron’s “information systems and mail accounts from some of his campaign managers.” It said the leaked data had been “fraudulently” obtained and that fake news was probably mingled in with it.

The commission urged French media and citizens not to relay the leaked documents. French electoral laws impose a news blackout Saturday and most of Sunday on any campaigning and media coverage seen as swaying the election.

The Macron team asked the campaign oversight commission Saturday to bring in cybersecurity agency ANSSI to study the hack, according to a government official who spoke to The Associated Press on condition of anonymity because they weren’t authorized to discuss the details publicly.

ANSSI can only be called in for cases where the cyberattack is “massive and sophisticated” — and the Macron hack appears to fit the bill, the official said.

Someone on 4chan — a site known, among other things, for cruel hoaxes and political extremism — posted links to a large set of data Friday night.

Macron’s team quickly confirmed that it had been hit by a “massive and coordinated” hack some weeks ago, in which unidentified hackers accessed staffers’ personal and professional emails and leaked campaign finance material and contracts — as well as fake documents — online.

In a cursory look at the leaked documents, they appear to be day-to-day communications, with a few items so out of character that they might be fakes. Other documents, which seem to date back several years, don’t appear related to the campaign at all.

Le Pen’s campaign could not formally respond due to the campaigning blackout, but National Front official Florian Philippot, asked in a tweet: “Will the #Macronleaks teach us something that investigative journalism deliberately buried?”

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The Macron hacking announcement came just 10 days after the campaign’s digital chief, Mounir Mahjoubi, said it had been targeted by Russia-linked hackers — but that those hacking attempts had all been thwarted.

Mahjoubi and other campaign staffers would not comment Saturday.

The documents leaked Friday were widely circulated on U.S. far-right sites. Experts dissecting the data say they spotted a couple of Russian names in the dump. Matt Suiche of cybersecurity firm Comae Technologies said “there’s Cyrillic script in the metadata,” but added it was hard to tell whether that’s due to carelessness or a deliberate misdirection.

In other voting issues, the French voting watchdog urged the Interior Ministry to look into claims by the Le Pen campaign of tampering with ballot papers in a way that favors Macron.

The first French territory to vote Saturday was Saint-Pierre-et-Miquelon, an archipelago near Newfoundland, where voters came dressed in scarves and jackets to ward off the chilly weather. Shortly afterward, voting started in French Guiana and the French West Indies, where voters wore shorts.

French citizens also turned out in droves to vote in the Canadian province of Quebec. The French consul general in Montreal said more than 57,000 people had registered to vote in the province, the vast majority in Montreal.

The last polling stations on the French mainland close at 8:00 p.m. Sunday, when the first pollsters’ projections and official partial results are expected.

The campaign has been unusually bitter, with voters hurling eggs and flour, protesters clashing with police and the candidates insulting each other on national television — a reflection of the country’s deep divisions.

Le Pen, 48, has brought her far-right National Front party, once a pariah for its racism and anti-Semitism, closer than ever to the French presidency, softening its message and seizing on working-class voters’ growing frustration with globalization and immigration.

The 39-year-old Macron, a former economy minister and investment banker who has never held elected office, also helped upend France’s traditional political structure with his wild-card campaign.

After ditching France’s traditional left-right political parties in a first-round presidential ballot, voters were choosing between Macron’s business-friendly vision and Le Pen’s protectionist, closed-borders view. Macron wants a strong EU, while Le Pen favors a France-first policy that could see France spin out of the bloc.

From depressed northern France to the streets of Paris, few voters seemed aware Saturday of the hacking attack on Macron’s team — although several were looking forward to the end of a vitriolic campaign.

In Henin-Beaumont in northern France, where Le Pen will cast her ballot on Sunday, 28-year-old Thomas Delannoy said the campaign “looks like reality TV.” The construction painter called the electoral process “laughable,” saying that neither candidate had a platform he could identify with.

Macron will vote Sunday in the seaside town of Le Touquet, where his wife Brigitte went for a walk Saturday with her daughter and grandchildren.

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Angela Charlton contributed to this report.