While reports have been swirling in recent weeks about the new handsets, this was the first with a precise date.
Apple did not immediately comment.
Re/Code said the event would be to announce Apple's next-generation iPhones, with screen sizes stretched to 4.7 and 5.5 inches and with a faster processor.
Apple sold some 35 million iPhone in the past quarter, lifted by growth in China, but its share of the smartphone market has been shrinking globally.
The research firm Strategy Analytics said the rival Android operating system captured 85 percent of the worldwide market in the second quarter, and is threatening to marginalize rival platforms.
Apple's global market share fell to 11.9% from 13.4% a year ago, according to that survey.
Samsung, which has been selling large-screen phones and a wide variety of other handsets, has become the world's largest smartphone maker with a 25 percent market share, according to analysts.
Apple typically updates its product cycle in the second half of the year, getting a lift from holiday sales.
Last year it unveiled the iPhone 5S and the lower-priced iPhone 5C in September, getting record sales at the launch.
Apple is working on a new operating system which allows for mobile payments and includes a health platform. The system iOS8 is expected to be in the new iPhones.
But some analysts say Apple needs to come up with a new innovation to keep leadership in the tech sector. Reports say Apple is working on a smartwatch and a new interactive television, but the company has said little about this.