Early official results have confirmed a landslide win for France's far-right National Rally, led by Marine Le Pen, more than doubling the vote share of President Emmanuel Macron's centrist group.

The resounding defeat led Macron to dissolve the National Assembly, the lower house of parliament, on Sunday and announce elections in just a few weeks' time.

The eurosceptic National Rally - which used to be called the National Front until six years ago - has softened its image in recent years in an effort to widen its appeal and strengthen Le Pen's bid for the presidency.

The party received 31.36 per cent of the vote in the European elections, according to preliminary results announced by the Interior Ministry early on Monday after all the votes had been counted.

Macron's camps came a distant second with 14.6 per cent. The Socialists came third with 13.83 per cent.

Another far-right party, Reconquete, won 5.47 per cent.

Macron's job as president is not at stake in the upcoming elections, as the next presidential election is not scheduled until 2027.

He aims to create a more stable majority for his remaining term of office. He will be hoping that citizens in France will not vote the same way in national elections as they did in the European Parliament elections and that the snap election will break Le Pen's momentum.

Macron's governing camp has not had an absolute majority in the National Assembly for two years.