Collection gathered by German advisers to Qing court being sold

Constantin von Hanneken was initially hired as one of Detring's military advisers and moved to China in 1879. He quickly established himself as a close friend and adviser of Li Hongzhang.

Von Hanneken was put in charge of reorganizing and modernizing the Chinese army in designing and building several naval forts, with the most significant being Port Arthur in Dalian, Liaoning province.

He rose to the rank of Chinese general and married Detring's eldest daughter, Elsa, in 1895. He died in 1925.

Among the items going under the hammer in the collection is an extremely rare blue and white double-gourd dragon vase with the Jiaqing seal mark and period (1796-1820), which is expected to fetch 300,000 pounds ($391,000).

A rare white glaze vase from the Qianlong period (1736-95) is on sale for an estimated 400,000 pounds.

Cherrei Tian, deputy director at Sotheby's Chinese department, said: "You have to be quite brave to leave it completely white, it means your eyes don't get distracted and your focus is entirely on the shape and the form, so the portion has to be absolutely perfect and it is in perfect condition."