Ford and Mazda are to spend an additional US$37.3m with their Chinese partner Changan on their engine plant venture.

The move follows a surge in sales of Ford cars, particularly the Focus.

The three companies will increase their investment in the engine plant in Chongqing city which produces engines for the Ford J53 and J36 models.

Ford's China car sales have risen in recent months as consumers spurn Japanese brands because of a lingering territorial row between China and Japan. The dispute has also benefitted other foreign automakers including General Motors, BMW and Hyundai.

Ford's sales in China jumped 48% last month from a year earlier, outpacing the 5.3% gain in the country's overall market. The new Focus, launched in late April, has been selling so well that workers at the Chongqing car plant have added shifts to keep up with demand.

The engine venture also makes engines for Mazda models.