Apple sends out invitations for the Sept. 10 even, where it is expected to unveil the iPhone 5S, iPhone 5C and the redesigned iOS 7. Reuters

While Apple (NASDAQ:AAPL) has made it official that it is holding a media event on Sept. 10 at 10:00 a.m. Pacific Time at its headquarters in Cupertino, Calif., where the company is expected to unveil the new iPhone 5S and iPhone 5C, a new report surfaced online on Tuesday, claiming that the new handset models have begun arriving in the United States.

MacRumors reported, on Tuesday, that Apple has started shipping at least some of the new iPhone models into the U.S. for immediate distribution to carrier partners, third-party retail partners and its own channels.

If Apple follows its previous release pattern, both the iPhone 5S and iPhone 5C would be released in the U.S. and in other key international markets in about 10 days from the Sept. 10 unveiling event. Rumors have it that the most likely release date for the new iPhones will be Sept. 20, which is a Friday -- also an Apple pattern.

The MacRumors report also pointed to C Technology, a Chinese website that posted a number of photos of alleged iPhone 5C boxes and manuals, and claimed that 1.2 million iPhone 5C units were shipped to the U.S. on Monday.

Apple's invites for its Sept. 10 event. Apple

Over the past few days, several images of alleged iPhone 5C units showed up on the Internet, suggesting the device is ready to be shipped to customers. The most recent leak is a set of new images from the Netherlands, which showed an instruction manual claimed to be of the Dutch version of the iPhone 5C.

According to AppleInsider, the alleged manual showed an iPhone with a black glass front and white plastic back, and running the iOS 7. The manual also highlighted standard iPhone features, such as a Lightning connector, home button, lock button, volume buttons and mute switch.

If current rumors are to be believed, it would seem that Apple has begun stockpiling new iPhone units in the U.S. However, it is still not known how many units of the new handsets will be released initially. DigiTimes reported, in August, that Apple may ship only three million to four million units of the iPhone 5S in the third quarter of this year, due to production delays of the fingerprint sensors.

Coming back to Apple’s invitation for the Sept. 10 media event, the graphics on the invite sent out by the company on Tuesday includes colorful circles behind a white Apple logo and a tagline: “This should brighten everyone’s day.”

While the invite doesn’t reveal any other details about the upcoming event or the new products to be unveiled, the colorful graphics suggest -- like widespread rumors have done so far -- that the iPhone 5C could be available in multiple color options. The iPhone 5S is also rumored to come out in a new champagne color option, in addition to the conventional black and white colors.