There is growing evidence that Apple Inc.’s latest iPhone is falling shy of its predecessor in China, suggesting a setback for the world’s most valuable company in its most important overseas market.

The iPhone 15 series saw a 6% decline in sales in its launch month compared with the prior year, according to data from market researcher GfK that covers end-consumer sales for all channels. Mobile industry tracker IDC estimates Apple’s shipments were down 4% in the third quarter, with both identifying Huawei Technologies Co.’s return to the mobile arena spotlight as a key event in the period. Huawei’s Mate 60 series recorded sales of close to 1.5 million in its launch month, more than doubling from a year ago, GfK said, despite facing supply constraints.