Apple has issued a warning on its support pages regarding iPhone 3G and iPhone 3GS overheating, marking the first time the company has officially acknowledged the problem. Reports that the iPhone 3GS is having overheating problems have surfaced last week, merely days after the devices was launched.

Over the last few days, many iPhone 3GS users have been reporting that Apple’s new iPhone 3GS is getting abnormally hot when used in various environments. PC World‘s Melissa J. Perenson noted in her report that she was experiencing the same phenomenon with her new 16GB iPhone 3GS.

Various U.S. gadget sites such as as Gizmodo and Engadget have circulated reports of the same problem, and PC World’s Tech Inciter David Coursey, a hot iPhone 3GS owner as well, was even discussing a possible iPhone 3GS recall from Apple. Others have even claimed a discoloration of the iPhone’s back cover due to the device running very hot.

Though Apple has not officially acknowledged a problem with the new iPhone 3GS, the company has now issued a warning on its support knowledge base, basically putting the blame on users. The warning prompts users not to leave their phones in a car because temperatures in parked cars can exceed the -20º and 45º C (-4º to 113º F) range the iPhone 3G and iPhone 3GS were designed to function in properly.

Apple says in the support article that “if the interior temperature of the device exceeds normal operating temperatures, you may experience the following as it attempts to regulate its temperature: the device stops charging, display dims, and/or weak cellular signal.”

Apple also posted an image (above) of an overheated iPhone screenshot with a message that appears when the operating temperature of the devices is too hot. The company says this is a safety mechanism that protects the components of the iPhone 3G/3GS.

Other conditions that Apple deems as possible overheating causes are: leaving the phone in direct sunlight for extended amounts of time or using certain applications in hot conditions or direct sunlight for a long time. An Apple overheating scenario is using GPS tracking in a car on a sunny day or listening to music while in direct sunlight.

Apple further advises hot iPhone 3G and 3GS owners to turn their device off when the above-mentioned temperature warning appears on screen and move it to a cooler environment, allowing the iPhone to cool down before resuming use.

Apple has sold over one million iPhone 3GSs since the device launched on June 19.