France's government yesterday faced a no-confidence vote that could spell the end of Prime Minister Michel Barnier's administration, plunging the country into uncharted waters.

The toppling of the Barnier government after just three months in office would present President Emmanuel Macron with the unenviable choice of picking a viable successor with over two years of his presidential term left.

The National Assembly lower house is due to debate two motions brought by the hard left and the far right in a standoff over next year's austerity budget, after the prime minister on Monday forced through a social security financing bill without a vote.

The motion brought by the far-right National Rally (RN) of three-time presidential candidate Marine Le Pen is expected to be rejected.

But Le Pen has said her forces would back the left's motion, giving it enough numbers to pass in an evening vote that could topple a French government for the first time in more than 60 years.

Macron was expected to wrap up his three-day state visit to Saudi Arabia and return to Paris later in the day.

Still a world away from the crisis, on Wednesday he strolled through the desert sands of the Al-Ula oasis, an iconic tourist project of the kingdom, marvelling at ancient landmarks.

On Tuesday, Macron accused Le Pen's far-right of "unbearable cynicism" in backing the motion.