The "Fifty Shades of Grey" phenomenon barrelled into France this week with sales of the bondage-fuelled erotic romance rivalling the Harry Potter franchise two days after its release.

Some 40,000 copies of the "mommy porn" hit -- which has sold some 40 million copies worldwide -- flew off the shelves on the day of its French release on Wednesday, according to publisher JC Lattes.

The FNAC megastore said it had sold 15,000 copies by Thursday, the highest sales for any book since the final instalment of J.K. Rowling's boy wizard series, "Harry Potter and the Deathly Hallows", in 2007.

Spiced up with sado-masochism, the 2011 novel by British author E.L. James is the first part of a trilogy about a relationship between a college graduate and a young business magnate.

Volumes two and three -- "Fifty Shades Darker" and "Fifty Shades Freed" -- will hit shelves in France early next year.

Rights to the series have been sold in more than 40 countries, despite lacklustre reviews such as The Guardian's which regretted its "improbable" dialogue, "lame characterisation" and "irritating tics".

"Facile, insipid, dull," was how the French edition of Cosmopolitan summed it up, deriding sex scenes so "overloaded with details that you are reminded more of a lesson in anatomy than a porno."