Theme park operator Six Flags Entertainment warned investors Friday that its years-long push to enter the lucrative Chinese market may collapse after its local partner defaulted on a payment. Shares in the Grand Prairie, Texas-based company plunged to levels not seen since 2014, coincidentally the same year Six Flags first announced its China expansion plans. While Six Flags continues to work with partner Riverside Investment, “the termination of all the Six Flags-branded projects in China” is a possibility, the company said in an SEC filing. Six Flags said in its 2017 annual report that it was developing eight parks in China, and announced three more in April, 2018. The company operates 26 parks across the United States, Mexico and Canada. Friday’s 18% drop was the largest ever for Six Flags, whose first park, Six Flags Over Texas, opened in 1961.