Hong Kong (CNN Business) After a tough 2018, global automakers look set for another bruising year.

Data published Monday show that the slowdown in China, the world's biggest car market, is getting worse. And the United States is considering imposing tariffs on imported cars, a move that would hit global brands hard.

General Motors GM Volkswagen VLKAF Passenger car sales in China slumped by almost 18% in January compared to a year ago, according to China's Association of Automobile Manufacturers. That's the latest ominous sign for global brands such asand, which have come to depend on blockbuster sales to Chinese consumers.

Sales in China's auto market turned negative in July last year and the slump has now extended into a seventh month. Annual car sales declined in 2018 for the first time in 20 years.

The world's second largest economy is feeling the effects of government attempts to rein in risky lending after a rapid rise in debt levels. Trade tensions with the United States and the removal of Chinese subsidies in the auto sector are making matters worse.

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