French campaign watchdog examines election-eve Macron leak

France's election campaign watchdog is investigating a hacking attack and document leak targeting presidential candidate Emmanuel Macron that his political movement calls a last-ditch bid to disrupt Sunday's tense runoff vote.

French President Francois Hollande on Saturday promised a response to the hacking of centrist presidential candidate Emmanuel Macron following the publication online of thousands of stolen emails from his campaign team.

"We knew that there were these risks during the presidential campaign because it happened elsewhere. Nothing will go without a response," he told AFP during a visit of a cultural institute in Paris.

Fears of hacking and campaign interference have simmered throughout France's high-stakes, closely watched campaign and boiled over Friday night as Macron's team said it had been the victim of a "massive and coordinated" hack.

His political movement said the unidentified hackers accessed staffers' personal and professional emails and leaked campaign finance material and contracts, as well as fake decoy documents, online.

The perpetrators remain unknown. While the hack is shaking up the already head spinning campaign, it's unclear whether the document

dump would dent Macron's large poll lead over far-right Marine Le Pen going into the vote. After ditching France's traditional left-right parties in a first-round election, voters are now choosing between Macron's business-friendly, pro-European vision and Le Pen's protectionist, closed-borders view that resonates with workers left behind by globalisation. The future of the European Union may hinge on the vote, also seen as a test for global populism.