A blue monochrome by French artist Yves Klein sold for 18.4 million euros (more than $21 million) on Thursday, auction house Christie's said, the most a Klein painting has ever sold for in France.

Measuring four metres across and nearly two metres high (13 by seven feet), "California (IKB 71)" is the largest monochrome painting by the artist in private hands, Christie's said.

Klein, who died in 1962 aged just 34 years old, patented the ultramarine hue of the special thick paint he developed for his paintings, calling the mix of synthetic resin, matte and pigment "International Klein Blue" or IKB.

The artist said that none of his monochromes resembled each other and were "of quite a different essence and atmosphere", according to Christie's.

He painted "California" in early 1961, shortly before he made his first and last trip to the United States for his debut exhibitions across the Atlantic, in New York and Los Angeles, it said.

Klein attached an array of small pebbles to the painting's surface, making it "evocative of a seabed beneath the blue abyss of an ocean", according to the auction house's description.

In 2013, a flower-like sculpture by Klein, made from blue-tinted sponges on a metal stem and stone base, fetched $22 million at Sotheby's in New York, breaking the auction record for his works.

The artist had explained once that his inspiration for the work, "Sculpture eponge bleue sans titre," was simply noticing the beauty of the colour blue in the sponges that he himself used in his studio while painting.