Establishing a joint ventrue to assemble the cars in China is seen as a way to avoid high import duties, as well as to catch onto incentives available only for Chinese EVs manufacturers.  With the restrictions in place today, there is currently no business model that supports volume sales for automobiles imported into China.

Apparently are just months away from the announcement of a joint venture partner because Tesla is in a hurry according to an interview by CEO Elon Musk to Engadget:

"… he  (Musk) aims to lock down manufacturing plans — finding a local partner and a location for the plant — for the local market by middle of this year. As with most other foreign auto makers who do business in China, this key strategy is to waive the high import duties charged by the local government, as well as to access other local incentives for EVs. Until then, Musk said there's no further news to share on that end."