Jade refers to two different materials: Nephrite Jade and Jadeite Jade.
There is no Jadeite source in China. Almost all Jadeite imported into China now is from Myanmar (Burma). In fact, till today, the only known source of coveted Imperial Jade (Greens & Lavenders) is Burma. Jadeite is relatively "new", in that it was only discovered in the late 17th to 18th century and made popular during the Qing (Ching) dynasty during the reigns of Emperor Qian Long.
On the other hand, Nephrite Jade has been known, revered and used in China from more than 5000 years. This is, even today, refered to as the True Stone of Heaven by the chinese. The main source of Nephrite desired by the chinese come from the Eastern Turkestan (Xin Jiang province). Eastern Turkestan covers 1.6 million square km, one sixth of the present Chinese territory. It is located in Central Asia, it is bordered by Kazakhstan to the north, Mongolia to the northeast, and Kyrgyzstan and Tajikistan to the northwest and west. This is where the famous KunLun mountains are located.
As in ancient times, the mutton-fat white variety of Nephrite jade is most valued. Rare colors like yellow, deep black and violets, bright greens, reds etc, as well as artistic carvings, especially two-color carvings (usually white and caramel-brown) are also valuable.
Hope that helps!
I LOVE Gemstones and Jade, and have been a collector for many years.