A photo taken on June 13, 2014 shows the outside of  an Apple store in Shanghai.

Apple Inc suppliers in China will begin mass production of its largest iPhones ever next month, according to people familiar with the plans, as the smartphone maker faces increased competition.

The tech giant is ramping up on two bigger devices, said the people, who asked not to be identified because the plans are private. One model will have a 4.7-inch display, compared with the 4-inch screen of the current iPhone 5s, that may be available to ship to retailers around September, said two of the people. A 5.5-inch version is also being prepared for manufacturing and may be available at the same time, the people said.

Apple is getting ready for its annual unveiling of new iPhones after rivals including Samsung Electronics Co and HTC Corp released smartphones with displays that are as large as 5.7 inches. Consumers have been gravitating toward larger-screen devices - in China, and 40 percent of mobile gadgets based on Google Inc\'s Android operating system that were sold so far in 2014 had display sizes of more than 5 inches, according to an estimate from Forrester Research.