I would say the easiest is to check the Jepp charts, whether paper or elec. (press the little blue "i" icon at the FIR and read the note, and see what the info says. As far as I remember, coming from the West (Almaty/Kazakhstan), you'd be entering Chinese FIR via Urumqi and they do NOT require any pre-entry clearance, nor do Russia. On the Jepp.'s it's really only Mongolia and Kazakhstan that still request a pre-entry clearance in general.. Anyways you'd better double check for yourself. Have fun.