This busker is playing an old Chinese instrument dating back at least to the Qin Dynasty (200 BC) called the ruan. This old form of pipa with straight-neck and round body was named ruan after a master player of this instrument, Ruan Xian, one of great scholars among "The Seven Gentlemen" in the 3rd Century.
The Ruan is used in Peking opera, as well as in modern Chinese orchestras. There is a family of ruan of various size with zhong (middle) ruan and da (big) ruan used similarly as the viola and cello in western orchestras.
If you'd like to hear the sound of the ruan, here is a lovely melody.
Posted for Mary's Sepia Scenes.