Tesla has said it wants to build electric cars in China to avoid a 25% tariff on imported vehicles.

The company did not provide a timeline for setting up a China plant, but said it expects to “more clearly define” its China production plans by the end of the year.

Tesla (TSLA) shares closed up 1.7% at $382.61 in Thursday trading.

China’s central government requires foreign companies such as Tesla to have a Chinese partner in new auto manufacturing ventures, with the foreign company owning no more than 50 percent.

Tesla did not say which companies it might partner with, sparking rampant online speculation. At least three companies—Shanghai Electric Group, Shanghai Lingang Holdings and Tianjin Motor Dies—reported in exchange filings that they were not in touch with Tesla about its plans in response to media reports implicating them.

Much of the speculation has centered on Tencent Holdings (TCEHY), the internet giant that is China’s largest company. Earlier this year, Tencent acquired a five-percent stake in Tesla for $1.8 billion.

Tesla has not said which vehicles it plans to build in China. However, a supplier familiar with the company’s thinking said it was considering the Model 3 sedan and a crossover companion called Model Y. The Model 3 is slated to begin production in July at Tesla’s Fremont plant in California, with the Model Y tentatively scheduled to follow in mid-2019.

In a separate but related development, U.S. Trade Representative Robert Lighthizer said on Thursday he was concerned about Ford Motor Co’s announcement earlier this week that it will move some production of its Focus small car to China and import the vehicles to the United States.

“If it happened for reasons that are non-economic reasons, then I think the administration should take action,” Lighthizer told U.S. lawmakers.

Tesla is the most valuable U.S. automaker, with a market capitalization of more than $60 billion, but it has yet to turn an annual profit.