General Motors Co and its Chinese joint-venture partners said on Wednesday they plan to build a $1 billion auto assembly plant in the city of Chongqing as part of its push to remain the leader in the world's largest auto market.

GM, SAIC Motor Corp <600104.SS> and Wuling Motors Holdings Ltd <0305.HK> said they will begin construction of the plant early next year pending relevant Chinese government approvals. The 6.6 billion Chinese yuan ($1.06 billion) first phase is scheduled to open in 2015.

The plant will have an annual production capacity of 400,000 vehicles and engines, although the partners did not disclose what vehicles will be built there.

The new plant is part of SAIC-GM-Wuling's push to reach its production target of 2 million vehicles per year by the end of 2015.

(Reporting By Ben Klayman in Detroit; Editing by Gerald E. McCormick)