There is nothing called "Northeast China". There is only "the Northest" - "dong bei" in Mandarin. Nobody says "dong bei Zhong Guo". 

Manchuria is just like the word Tibet. Nobody call it Xizang or the West Land as its Chinese name really means.

Aranherunar, it is true that more and more people in Manchuria use the term "Manchuria (Manzhou in Mandarin) nowadays.