Emails from the campaign of French presidential candidate Emmanuel Macron have been leaked to a file sharing site, throwing the race into chaos in the lead up to Sunday's vote.

The emails originated from Macron's political party, En Marche! (Onwards!), and comprised nine gigs of data.  The French press is prevented by law from publishing any information that might sway the election, so very little detail of what was in the emails has been posted.

Reuters:

"The En Marche! Movement has been the victim of a massive and co-ordinated hack this evening which has given rise to the diffusion on social media of various internal information," the statement said.

An interior ministry official declined to comment, citing French rules that forbid any commentary liable to influence an election, which took effect at midnight on Friday (2200 GMT).

The presidential election commission said in statement that it would hold a meeting later on Saturday after Macron's campaign informed it about the hack and publishing of the data.

It urged the media to be cautious about publishing details of the emails given that campaigning had ended, and publication could lead to criminal charges.

Comments about the email dump began to appear on Friday evening just hours before the official ban on campaigning began. The ban is due to stay in place until the last polling stations close Sunday at 8 p.m. (1800 GMT).

Opinion polls show independent centrist Macron is set to beat National Front candidate Le Pen in Sunday's second round of voting, in what is seen to be France's most important election in decades. The latest surveys show him winning with about 62 percent of the vote.

Former economy minister Macron's campaign has previously complained about attempts to hack its emails, blaming Russian interests in part for the cyber attacks.

On April 26, the team said it had been the target of a attempts to steal email credentials dating back to January, but that the perpetrators had failed to compromise any campaign data.

The Kremlin has denied it was behind any such attacks, even though Macron's camp renewed complaints against Russian media and a hackers' group operating in Ukraine.

Vitali Kremez, director of research with New York-based cyber intelligence firm Flashpoint, told Reuters his review indicates that APT 28, a group tied to the GRU, the Russian military intelligence directorate, was behind the leak. He cited similarities with U.S. election hacks that have been previously attributed to that group.

If I were Putin and wanted to influence the French election, I would have leaked these emails a week ago, not less than 48 hours before the election, when it would be illegal for the press to comment on them.  I think this fact alone argues against a Russian government conspiracy.

There's the chance that Putin knew this and leaked them anyway to damage Macron after he takes office.  But would the effort to hack the party's emails be worth it for such a shot in the dark?

As it stands, it wouldn't have made any difference anyway.  Macron's lead is pretty comfortable.  It would take a polling error of "gargantuan" proportions for him to lose to the National Front candidate, says Nate Silver.

In the age of Trump, pollsters make such predictions at their own peril.