With slowing sales and increased competition in the world's largest car market, a strong presence at the Beijing auto show that opens today is crucial for Detroit's automakers.

The sheer size of the market -- with 1.35 billion people and a growing middle class with its own set of soccer moms -- means a leader like General Motors cannot afford to let up and stragglers like Ford and Chrysler need to spend and grow quickly.

That means more investment and release of a slew of new and enticing models at this year's show to compete in a market that sold 18.5 million vehicles last year and that some predict could move 35 million vehicles annually by 2020.

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