It comes as the US technology giant is facing fierce competition in the country from local rivals.
During the same period China’s Huawei saw its sales jump by 64% in its home market, the report says.
Apple (NASDAQ: AAPL) and Huawei did not immediately respond to requests for comment from the BBC.
Aside from a resurgence of Huawei sales at the more expensive end of the Chinese phone market, Apple was also “squeezed in the middle on aggressive pricing from the likes of Oppo, Vivo, and Xiaomi,” Counterpoint Research’s Mengmeng Zhang wrote.
China, which is one of Apple’s biggest markets, also saw overall smartphone sales shrink by 7% in the same period, the report said.
Huawei struggled for years due to US sanctions but its sales surged after releasing its Mate 60 series of 5G smartphones in August.
It came as a major surprise as the Chinese firm was cut off from key chips and technology required for 5G mobile internet.
Honor, which is the smartphone brand spun off from Huawei in 2020, was the only other top-five brand to see sales increase in China during the period, according to the report.
Sales of Vivo, Xiaomi, and Oppo also fell in the first six weeks of the year, Counterpoint said.
Its report also said Apple’s share of the Chinese smartphone market dropped to 15.7% from 19% last year, putting it in fourth place as it fell from the number two spot.
Meanwhile, Huawei rose to second place as its market share grew to 16.5% from 9.4% a year earlier.
Despite its sales falling by 15% over the last year, Vivo remained China’s top-selling smartphone maker, Counterpoint said.
Apple started offering discounts on its official sites in China last month before subsidising certain iPhone models through its flagship stores on Alibaba’s marketplace platform Tmall last week.
A slowdown in demand in China could affect Apple’s revenue which already disappointed investors when the firm released its earnings last month.
The firm said sales in China were $20.82bn (£16.4bn) in the last three months of 2023, down from $23.9bn in the previous year.
Apple shares fell by 2.8% in New York trade on Tuesday.
