Marine Le Pen's far-right National Rally (RN) party scored historic gains to win the first round of France's parliamentary election on Sunday, exit polls showed, but the final result will depend on days of horse trading before next week's runoff.

The RN was seen winning around 34% of the vote, exit polls from Ipsos, Ifop, OpinionWay and Elabe showed, in a huge setback for President Emmanuel Macron, who had called the snap election after his ticket was trounced by the RN in European Parliament elections earlier this month.

The RN's share of the vote was comfortably ahead of left-leaning and centrist rivals, including Macron's Together alliance, whose bloc was seen winning 20.5% to 23%.