Valerie Trierweiler, the girlfriend of French President Francois Hollande, has been hospitalised, aides said, two days after he was reported to be having an affair.

Aides to the "first girlfriend" said she had been admitted "for a rest and to undergo some tests," and was expected to leave hospital tomorrow.

Closer magazine reported on Friday that Mr Hollande has been having an illicit affair with actress Julie Gayet.

Photos in a celebrity magazine published on Friday purporting to show a nocturnal visit by Mr Hollande to a mistress risk stealing the show on Tuesday when he faces media for up to two hours in the traditional start-of-year news conference.

Mr Hollande's office has complained of breach of privacy but issued no denial. 

The saga took a new turn today when it emerged his official partner, 48-year-old ex-journalist Valerie Trierweiler, had been hospitalised hours after the magazine hit newsstands.

The coming weeks will tell whether Francois Hollande can pick up the pieces of his accident-prone presidency and start to pull the euro zone's second-largest economy out of decline. It may be his last chance to do so.

The new year could hardly have started worse for the French leader, who failed to keep a promise to the nation to halt the rise in unemployment by the end of 2013 and is now dealing with media allegations of a secret love affair.     

Yet with polls showing most French are blasé about his private life, the real question is whether he will use the media event to show he is ready to tackle the double burden on the French economy: rising taxes and public spending.