William Klein + Daido Moriyama, Tate Modern, London

Here are two photographers, one American, the other Japanese, in pursuit of what it is to represent the urban scene. Their two exhibitions seem to form a part of a single quest – there is no sudden moment at which Klein (b.1928) stops and Moriyama (b.1938) appropriates the wall spaces of Tate Modern.

It is if the curators want us to see them as sequential or even complementary visions. And yet there are dramatic differences, in tone and feel. Klein's show begins with a hectic photomontage and a film of the neon lights of New York, complete with rhythmic syncopation.

Klein's vision is a rumbustious, hectic, noisy one from start to finish. Everything comes at you pell-mell, at a rush, sometimes blurrily blinking like neon signage - which is one of his obsessions.

Images bank up against other images, cities against other cities: Paris, Rome, Moscow, Peking, New York. He squeezes out each one's manic essence. This is essentially a vision of the singularity of individuals, and all in furious motion, tongue-rasping, gun-toting, dancing, squirming. Klein's talent is perpetually restless – he moves through photography, abstract painting (which seems to emerge from calligraphy), fashion shoots, feature and documentary films.

Then, in his last room of all, he blows up a single photographic frame and paints over and around it, merging photography and painting. He feels like a documentor of the now, which never stops coming. Everything he sees he responds to with a huge exclamation mark of wonder. There is nothing aesthetically set apart or sadly ruminative about his work, no sense of the essential aloneness of the urban space. In short, nothing of the manner of Cartier-Bresson.

Moriyama, his junior by a decade, feels positively inward by comparison. He does not move into other disciplines. Instead, he digs more deeply into his own, exploring the formal possibilities of photography – how the simplest object can be made anew by the play of light and dark; how quickly an object can be persuaded to dissolve into abstraction.

His images often look so poignantly fleeting, sombre and hauntingly unstable. His cities are estranging places. The eye of the camera feels wary – in fact the single image that seems to summarise his quest and his character is one of a stray dog, snapped in 1971, that seems to turn upon its photographer even as he tries to capture it.