PARIS — 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.

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.