The so-called iWatch will debut alongside the iPhone 6, which is also expected to be unveiled that day with two screen sizes: 4.7 inches and 5.5 inches. (The iPhone 5S has a 4-inch screen.)
Paczkowski had previously reported that the iWatch might come out in October, but it appears Apple has bumped up its plans.
Apple's wearable will likely have HealthKit and HomeKit integration, enabling users to track their health and fitness and use the wearable to control other smart devices at home.
Apple hasn't yet sent out invites to the Sept. 9 event. It usually announces product launches about a week before they happen.