French presidential candidate Emmanuel Macron's campaign has complained of being the victim of a "massive and coordinated hacking attack", a statement said.
The socio-liberal candidate's team issued the statement late on Friday saying the hacking has lead to the diffusion of "various internal information" on the social media, Xinhua news agency reported.
The leakage happened within the final hours of the last campaigning day. Macron is to face off with far-right candidate Marine Le Pen in a runoff vote on Sunday.
A large trove of documents were released online earlier Friday including emails, accounting documents and contracts from the campaign of the centrist candidate.
The files were posted anonymously on a sharing website and the person responsible for the posting remained unidentified.
Macron's political movement En Marche! (On the Move) later confirmed that it has been hacked.
"The files circulating were obtained several weeks ago by hacking into private and public mailboxes of several leaders of the movement," said the statement.
It also said the leaked documents only showed the normal functioning of a presidential campaign, but the files posted online mixed authentic documents with fake ones to sow "doubt and misinformation".
"It is not a simple hacking operation but an attempt to destabilise the French presidential election," said the statement, adding that it would "take all necessary initiatives with public and private actors" to clarify the incident.
Macron has maintained his position over Le Pen, according to surveys conducted by French pollsters.
The latest poll released on Thursday by the French Institute of Public Opinion showed that 61 per cent of votes will go to Macron and 40 per cent to Le Pen, consistent with the poll conducted before.