All About Shanghai
Appendix 1 - Police Powers

A further definition of the operative organizations for the policing of the International Settlement than is contained in the main body of this book (see Chapter Two, "Governments of Shanghai," under sub-heading, "French Procedure") seems advisable on the basis of information received from responsible officials of the Shanghai Municipal Council.
While it is true, broadly speaking, that police authority is vested in the respective organizations of the French Concession and the International Settlement there are other agencies exercising the right of arrest within certain limitations.
The Japanese Government maintains in the International Settlement a considerable staff of Consular Police, at times estimated as high as 250. They do not interfere with the Municipal Police in the general police administration of the Hongkew district, but they do upon occasion arrest their own nationals on warrants issued by the Japanese consular authorities without reference to the Municipal Police.
The Marshal attached to the United States Court for China is empowered to execute warrants of arrest on American citizens issued by the American authorities without reference to the Municipal Police.
To quote our authority: "Under the extraterritorial rights possessed by the Treaty Powers, there appears to be no question of their authority to exercise certain police functions over their own nationals in this Settlement."
The various Powers who have military or naval forces stationed in Shanghai often have military or naval patrols who function in the Settlement and deal with their own enlisted men at times irrespective of the Municipal Police.