French President Emmanuel Macron's chief of staff, Alexis Kohler, is under investigation for alleged influence-peddling and conflict of interest.

Anti-corruption prosecutors in France have launched a financial investigation into President Emmanuel Macron's chief of staff, Alexis Kohler, over allegations of influence-peddling and conflict of interest.

The probe was opened on Monday after anti-graft group Anticor lodged an official complaint accusing Kohler of breaching civil service rules over his family ties to the Mediterranean Shipping Company (MSC) while in public office.

The 45-year-old has family ties to the Aponte family, who founded MSC in 1970 and promoted it into a global leader in container shipping and cruise holidays.

The French investigative website Mediapart was the first to reveal Kohler's family links to the firm and transparency campaign group Anticor said its legal complaint was largely based on an investigation published by the news website.

Kohler served as a senior civil servant in France's economy ministry between 2012 and 2016. He left the job afterwards and joined Geneva-based MSC as finance director but continued to work on Macron's bid for the presidency in his spare time, providing advice on policy and strategy.

Under French law, civil servants can put their public sector careers on hold in order to work in the private sector for a limited number of years before returning to public administration.

Macron's office denounced the allegations against Kohler as "completely unfounded," and said the complaint lodged by Anticor stemmed from media reports that contained erroneous information.

Macron's office also noted that Kohler had at no time hidden his family ties to the Aponte family.

Kohler, who is the incumbent French president’s closest confidant, was once described by an aide who knows both men as "the last person Macron talks to at night and the first one in the morning."