PARIS (Reuters) - French Socialist Party heavyweight Bertrand Delanoe on Wednesday said he would back centrist Emmanuel Macron’s presidential bid to stop far-right leader Marine Le Pen from winning, as the roller-coaster election further shook the political landscape.

Emmanuel Macron, head of the political movement En Marche !, or Onwards !, and candidate for the 2017 French presidential election, attends a meeting with small business leaders in Puteaux, France, March 6, 2017. REUTERS/Charles Platiau

In a French election like no other, alongside a series of botched rebellions against conservative candidate Francois Fillon, the other major mainstream party, President Francois Hollande’s ailing Socialist Party, is facing its own splits.

The announcement by Delanoe, the popular former mayor of Paris, was a further blow to the Socialist candidate Benoit Hamon, who is lagging in fourth place in polls with little hope to qualify for the May 7 two-way second round.

“We need to support the candidate who can beat Marine Le Pen,” Delanoe told France Inter radio. “It wasn’t an easy decision to make (but) fighting the far-right has to be a priority. The useful vote for the (April 23) first round is a vote for Macron.”

Delanoe’s announcement came after a week of nearly daily warnings from Hollande and Socialist prime minister Bernard Cazeneuve over the risk of a far-right victory, and as more Socialist veterans are said to be tempted to jump ship.

Hamon, who is very much to the left of the Socialist Party, became his party’s candidate when he won primaries in January, but has been struggling to make his campaign take-off, while Macron, an independent centrist who used to be Hollande’s economy minister, is now the opinion polls’ favorite.

Earlier this week, the lower house of parliament’s president Claude Bartolone also pointed to Le Pen’s strength in polls when saying he was finding it hard to back Hamon and could be tempted to back Macron.

Opinion polls forecast that Le Pen will top the first round but Macron would easily beat her in the second round.

Some 46 days before the first round, however, analysts warned victory was not a certainty for Macron, given the possibility that Fillon, who on Monday received his party’s backing despite the financial scandal he is embroiled in, could see a ratings boost.

“It is too early to consider we will definitively have a Macron-Le Pen second round,”said Francois Miquet-Marty of Viavoice pollsters.

“Francois Fillon can still make a come back and Macron can still tumble,” he said, stressing that only about half of Macron’s voters were sure of their choice, versus 70-80 percent for Le Pen and 60-70 percent for Fillon.

Macron also finds himself under more media scrutiny now.

The organization of a costly promotion event for French entrepreneurs at the CES electronics show in Las Vegas by the Business France public agency while he was economy minister is being investigated by a watchdog, Le Canard Enchaine said.

Finance Minister Michel Sapin told Reuters Macron had nothing to do with it but Christian Jacob, a lawmaker for Fillon’s The Republicans party, said the financial prosecutor’s office should look into it.

Macron’s spokesman said he would sue Jacob for libel. The prosecutor’s office said it had asked finance ministry investigators for more information and would then decide whether to follow up.