French President Emmanuel Macron was in danger of falling short of a parliamentary majority after a first round of voting on Sunday, with some polling firms seeing his centrist alliance scoring less than the 289 seats required.
Macron's Ensemble (Together) alliance ran neck-and-neck with a new leftwing alliance, NUPES, with both scoring around 25-26 percent of the popular vote.
Extrapolating from these figures, polling firms projected that Ensemble would win 225 to 310 seats in the second round of voting next Sunday, possibly short of a majority.
NUPES, a newly unified leftwing alliance of leftists, Socialists, Greens and Communists, was seen as winning 150 to 220 seats, making them by the far the biggest opposition force in parliament.
If Macron's coalition falls short of a majority, it is expected to lead to messy bill-by-bill deals with right-wing parties in parliament, or he would have to try to poach opposition or independent MPs for his political grouping.
"It's a very serious warning that has been sent to Emmanuel Macron," political scientist Brice Teinturier told France 2 television. "A majority is far from certain."
Sunday's vote followed presidential elections in April in which Macron secured a second term, beating far-right leader Marine Le Pen with pledges to cut taxes, reform welfare and raise the retirement age to 65 for most people.
After a dismal performance in that vote, the French left has united behind Jean-Luc Melenchon, a hard-left veteran who has a radically different programme, including lowering the retirement age, wealth taxes and hiking the minimum wage by 15 percent.
Turnout was on course to be a record low of 47 to 47.5 percent, polling firm projections showed.
"Some people say that parliamentary elections aren't important but that's not true," Arnaud, a 40-year-old engineer, told AFP as he cast his vote in Paris. "If the president doesn't win a majority he can't get anything done."
Le Pen's far-right National Rally was seen as winning 10 to 45 seats nationally, potentially sharply increasing the party's representation in parliament from its current eight seats.
- Record low turnout -
The record-low turnout of below 50 percent is set to confirm the trend of dwindling interest for parliamentary elections over the past 20 years.
"The very personal nature of the presidential election still continues to interest people, but it overshadows all the other types of ballot, even the essential one which is electing the members of the national assembly," said Mathieu Gallard of the Ipsos polling group.
While Macron and his European Union allies breathed a heavy sigh of relief after his solid, if unspectacular, presidential victory against Le Pen, the last weeks have brought no sense of a honeymoon.
Energy and food prices are soaring in France as elsewhere in Europe, the treatment of English fans at the Champions League final in Paris damaged France's image abroad, and Macron has been accused by Ukraine of being too accommodating to Russia.
His new Disabilities Minister Damien Abad has faced two rape accusations -- which he has vehemently denied -- while new Prime Minister Elisabeth Borne has yet to make an impact.
Macron has made clear that ministers who are standing in the election -- including Borne, who arrived on top Sunday in her first attempt at winning a seat -- will have to step down if they lose.
Europe Minister Clement Beaune, a close ally of Macron and a crucial influence over France's Brexit and wider EU policies, is also standing in his first election and is seen as in a close fight with a left-wing rival.
Under France's system, a candidate needs over half the vote on the day as well as the backing of at least 25 percent of registered voters in a constituency to be elected outright in the first round.
Otherwise the top two candidates in a constituency, as well as any other candidate who won the backing of at least 12.5 percent of registered voters, go forward to the second round, where the candidate with the most votes wins.