BMW , the world's largest luxury carmaker, plans to invest nearly $900 million in its Spartanburg plant in South Carolina by 2014, boosting capacity to 350,000 vehicles in the mid-term.

This is in response to rising global demand for our BMW X models and the expansion of the BMW X family to include the BMW X4, BMW production boss Frank-Peter Arndt said in a statement on Thursday.

The X4 would be the fifth sport utility vehicle (SUV) in the BMW brand's model range. Three of the other four are also produced in Spartanburg, while the BMW X1, the smallest in the range, is built in Leipzig, Germany.

The expansion, which is Spartanburg's fifth, will bring BMW's total investments in its U.S. plant to nearly $6 billion.

The U.S. plant is one of BMW's fastest growing factories. Output rose 73 percent to 276,065 vehicles last year.

Increasing its capacity to 350,000 would mean it becomes one of BMW's biggest plants worldwide next to Dingolfing in Germany, where some 340,000 vehicles were manufactured in 2011.

(Reporting by Christiaan Hetzner)