Mazda soon will become the U.S. market’s only mass-market, non-luxury brand to be import-only.

The auto maker today announces it is ending Mazda6 production in Flat Rock, MI, by consolidating output at its plant in Hofu, Japan. Mazda has built the midsize car in Flat Rock, home to its Auto Alliance International joint-venture with Ford, since 2002.

The move, slated for the end of the current car’s run, is intended to “improve production and investment efficiencies and optimize business,” Mazda CEO Takashi Yamanouchi, says in a statement.

“The decision was made after carefully assessing all risks and opportunities, including global needs, changing demand in North America and exchange rate exposure,” he adds.

The Mazda6 has faced stiff competition. In 2010, the car’s deliveries totaled 35,662, good for 11th place among midsize cars, as defined by Ward’s segmentation. The segment leader was the Toyota Camry, which recorded a whopping 327,804 deliveries in the same time period.

Through May, the Mazda6 ranked 12th with 13,604 sales.

Mazda gets two of its nine U.S.-market models, the Mazda6 and Tribute cross/utility vehicle, from U.S. plants. The Tribute is produced at a Ford plant in Kansas City, MO, alongside its Ford Escape platform-mate.

Ford is replacing the Escape with an all-new model, but there are no indications of a Mazda platform-mate.

Mazda spokesman Jeremy Barnes declines comment on timing of the Mazda6 production move.

However, a next-generation Mazda6 is due for the ’14 model year, according to a product program timeline compiled by Ward’s.

Mazda started selling U.S.-built vehicles in 1987. From 1995 through 1999, more than 50% of its sales were local production, according to Ward’s data.

Output of a hybrid version of the Tribute ceased two years ago, while the Mazda B2000, a small pickup based on the Ford Ranger, was discontinued at the end of the ’08 model year.

AAI has seen its output decline over the past five years, dropping from 272,632 units in 2005 compared with 122,754 in 2010, according to Ward’s.

Mazda is mum on the future of AAI, saying only it will work with Ford to “identify potential opportunities for the plant” and “both companies remain committed to continuing this strategic partnership.”

Calls to Ford for comment were not immediately returned.

Ford in 1996 held a 33.4% controlling interest in Mazda, but steadily has reduced its stake. Ford’s stake in the auto maker now is less than 4%.

Luxury/specialty brands Audi, Porsche, Volvo, Jaguar, Land Rover, Smart, Fiat, Infiniti, Saab, Lexus and Mini sell vehicles in the U.S., but their respective volumes account for less than a 1% share of the light-vehicle market.

Through May, Mazda delivered 103,072 vehicles in the U.S. for a 2.0% share, according to Ward’s. In 2010, the brand accounted for 3.1% of the market on sales of 356,268 vehicles.