Attempting to turn off or reset the console during installation will reportedly "brick" the machine, rendering it unusable.
Downloading the update, which weighs in at around 1GB according to Eurogamer, activates online features such as Miiverse, Wii U Chat, Nintendo TVii (North America) and the system's eShop.
The update reportedly takes up to two hours to download, leading LA Times reporter Ben Fritz to unplug the device and "brick" the machine.
Writing about his experience on Twitter, Fritz said: "Warning: don't unplug your Wii U during the 2 hour plus software update or the console stops working."
Fritz said that there was no explanation and no cancel button, just a "super slow" progress bar.
"Seriously. I never played a single game and now as far as I can tell its unusable," he added.
Gallery: View images of the Wii U's launch lineup:
Copyright: NintendoThe Wii U is available now in North America and November 30 in Europe. A basic and premium edition will be available, as well as a European-exclusive ZombiU bundle.
The basic pack includes a white Wii U console with 8GB of memory, a Wii U GamePad, an AC adapter and an HDMI cable.
The Premium set will offer the system in black with 32GB of memory, a copy of Nintendo Land, Wii U sensor bar, a GamePad charging cradle, stands for the GamePad and console and Nintendo Network Premium membership.
Nintendo recently detailed how external hard drives will work with Wii U, while also revealing that only 3GB of the Wii U basic model's internal hard drive can be used, or 25GB of the Deluxe system's hard drive.
Further system details and an unboxing were recently revealed by Nintendo.
> Read Digital Spy's review for New Super Mario Bros U
> Read Digital Spy's review for Nintendo Land
Watch Digital Spy's Wii U hands-on video below: