Apple's newly-announced iPhone 6 and iPhone 6 Plus have gone up for pre-order on Friday, Sept. 12, in what seems like a rocky launch already.

Many interested buyers are currently unable to access the Apple Online Store to order one of the new smartphones. At the same time, some models appear to be selling out despite these availability issues. As expected, carrier websites are affected in particular, as they typically receive less stock.

Pre-orders for the iPhone 6 and iPhone 6 Plus have gone live in several countries worldwide, including the U.S., the UK, Canada, France, Germany, Hong Kong, Japan, Puerto Rico, and Singapore. Due to the aforementioned supply issues and technical problems, users in some areas may be unable to access the website or the app.

In the U.S., carriers such as AT&T, Verizon, and Sprint have started taking pre-orders for the device, while T-Mobile pre-orders still haven't gone live despite the fact that they're scheduled to start on Sept. 12 as well. At the time of writing, T-Mobile's website still allows only for pre-registrations, not pre-orders. The new iPhones will also go up for pre-order at retail stores such as Best Buy, Target, and Walmart, on Sept. 12.

As a reminder, Apple is selling the iPhone 6 in 16, 64, and 128GB internal storage configurations for $199, $299, and $399, respectively, on-contract. The iPhone 6 Plus is also available in 16, 64, and 128GB capacities, for $299, $399, and $499, respectively, on-contract. Pricing off-contract starts at $649 for the iPhone 6 and $749 for the iPhone 6 Plus.

The larger iPhone 6 Plus seems to be in higher demand and supplies appear to be limited already, with AT&T and Verizon pushing their shipping estimates for 14 to 21 days on several models.

Both the iPhone 6 and the iPhone 6 Plus will become available in stores next Friday, Sept. 19, and the first batch of orders should also hit customers on that same date. This year, Apple is also allowing in-store pickup for pre-orders of its latest iPhones.

It's worth pointing out that Apple's website is still down at the time of writing, but the company should fix issues soon and resume pre-orders. Did you manage to place a pre-order for an iPhone 6 or iPhone 6 Plus?