The Paris prosecutor's office is investigating suspected irregularities in the organisation of a high-profile trip to Las Vegas by President Emmanuel Macron when he was a French government minister.

The prosecutor's office said a formal judicial inquiry was opened on Friday 7 July into the case after a preliminary anti-corruption probe into the organisation of his 2016 trip to the Consumer Electronics Show.

The inquiry is for "favouritism" but does not name a suspected perpetrator yet, leaving it to investigators to determine later who might be at fault. Macron, 39, was economy minister at the time and used the trip to promote French technology startups.

The company tasked with organising the trip is believed to have won the contract without going through proper open tender procedures, among other suspected problems.

Macron was economy minister under the Socialist president Francois Hollande, who chose to stand down in April rather than fight again after his popularity collapsed.

He left the Hollande government to form En Marche!, a new political movement which surged to power in just a year. Macron won the French presidential election in May 2017 after fighting off the far-right Front National candidate Marine Le Pen. He became the youngest ever French president.

A month later, En Marche stormed to a landslide victory with its centrist platform in the French legislative elections, on a record-low turnout, taking a large majority of the seats in the National Assembly.

During his presidential campaign, Macron, a former investment banker, faced accusations of financial impropriety and hoarding vast wealth offshore in secret accounts, which he strongly denied and said were a deliberate attempt to defame him.

He asked the French authorities to investigate the rumours, which surfaced online, and dismissed them as "fake news and lies", suggesting it may have been part of an attempt by Russia to undermine his campaign in favour of the Kremlin's preferred candidate, Le Pen.

Emmanuel Macron
French President Emmanuel Macron at the start of the "retreat meeting" on the first day of the G20 summit in Hamburg, Germany, July 7, 2017REUTERS/John MACDOUGALL/POOL