A new Apple iPhone 6 Plus is seen during an Apple event at the Flint Center in Cupertino, California, September 9, 2014. [Photo/Agencies]

Smartphone sales in China, the world's biggest market for the devices, fell in the second quarter for the first time, market research firm Gartner Inc said on Thursday.

Sales of smartphones in China declined 4 percent in the quarter, the first year-over-year fall, the company said.

"China has reached saturation — its phone market is essentially driven by replacement, with fewer first-time buyers," said Anshul Gupta, research director at Gartner.

The country accounted for about 30 percent of total smartphones sales during the second quarter, according to the report.

Gartner also said worldwide smartphone sales grew at the slowest pace since 2013.

Still, Apple Inc's share of the worldwide smartphone sales market rose to 14.6 percent from 12.2 percent a year earlier.

Total iPhone sales in China soared 68 percent to 11.9 million units, Gartner said.

Apple's big-screen iPhone 6 and 6 Plus, which shattered iPhone sales records when they were launched, are about 11 months old.

Rival Samsung Electronics Co Ltd's share of the global smartphone market fell to 21.9 percent from 26.2 percent, Gartner said.

Despite the new S6 models, which it released in April, Samsung's premium phones continued to be challenged by Apple's large-screen iPhones, the report said.

Huawei Technologies Co Ltd, the fourth-largest smartphone maker globally, recorded the highest sales growth rate of 46.3 percent due to strong international sales and 4G smartphone sales in China.

Apple's shares were down about 2 percent in early trading on the Nasdaq.