French left pulls off election gamble, but unity going forward not so easy

• Left wing alliance more than triples 2017 seats
• Alliance has divisions over Europe, nuclear energy
• Majority sees chance to get moderate left support

France's new left-wing bloc is set to become the largest opposition force in parliament, but staying united will present an early test as President Emmanuel Macron's majority seeks allies on the moderate left to push through his reform agenda.

Macron was on course to lose his absolute majority in the National Assembly after projections pointed to a hung parliament that would see the leftist Nupes alliance winning 175 to 200 seats, almost tripling the score of its combined parties in 2017.

The bloc brings together the hard-left La France Insoumise (LFI), the Socialist Party, the Greens and Communists for the first time in 20 years - under the helm of the eurosceptic far-left veteran Jean-Luc Melenchon.

It campaigned to lower the retirement age from 62 to 60, raise the minimum wage and cap prices on essential products. But within the alliance there are major differences, from Europe to nuclear energy and policing, that were put aside for campaigning but which will be targeted by opponents.

"The rout of the presidential party is complete and no clear majority is in sight," Melenchon told his cheering supporters. "It is the failure of Macronism and the moral failure of those who lecture us."

Clementine Autain, one of his top lieutenants, said the results were a vindication of the left's strategy.

"This is a gathering of the forces for a social and ecological transformation on the basis of a profound change of society," she said.

Beyond the triumphalism, the question now is whether the alliance can hold. Melenchon's LFI party, which is projected to win about 90 lawmakers, slightly fewer than forecast in opinion polls, will want to lead the left in parliament.

But with the Socialists and Greens able to create their own parliamentary groups, it is not a given that they would support LFI on all issues when opposing the majority.

Senior Macron officials were on Sunday already trying to drive a wedge through the different factions of the Nupes alliance, accusing LFI of being a party of the extremes and an unconstructive force in parliament over the last five years.

"How many times did you join the National Front in parliament?" Justice Minister Eric Dupont-Moretti asked LFI stalwart Manuel Bompard on France 2 television. "The extremes join each other."

Corinne Narassiguin from the Socialist Party, which has given France two presidents since World War Two and been a driving force for European integration, said time would tell if the alliance would survive or had just been an electoral machine.

"Like in other coalition groups in Europe, we will agree on points and have points of difference," she told Reuters. "It is an experiment, it is the first time that we've had a group elected as an inter-group and it is our responsibility to voters (to keep it together)."

In a sign of how the ruling majority may act in the coming days, government spokesperson Olivia Gregoire offered an olive branch to some opponents.

"On the right and left, there are moderates, Socialist moderates ... there are people who on some draft legislation they will be beside us," she told France 2. "It's an open hand to all those who want to make the country move forward."