BEIJING — To most Americans, the names are unfamiliar, maybe a little hard to pronounce: Huawei, Xiaomi, Oppo, Vivo.

They are China’s biggest smartphone brands. Around the world — although not in the United States — they are making the handset business brutally competitive. This week, after Apple warned of disappointing iPhone sales in China, industry observers said that devices from the Chinese brands were a major culprit.

As the phone market in China reaches saturation and sales shrink over all, the country’s hardware makers are pushing hard, and increasingly winning fans, in places like France, Germany, India and Southeast Asia, where consumers find that the phones can do just about everything an iPhone can do at a fraction of the cost.

Apple sits comfortably atop the market in many countries, including China, for the highest-end handsets. But companies like Huawei have started to do elsewhere what they have done in China, competing with the iPhone on experience and value and luring customers with price comparisons that make them rethink buying Apple’s signature product.