BootMii NAND Backup Freeze?

I (accidentally) started up a NAND backup in BootMii, but it's been stuck on the same block for a few hours now, so I assume it froze for some reason. Is it safe for me to power off my Wii? It looks like there's a image that warns not to power off the system, so I'm not sure what to do. Any help would be greatly appreciated!

If it's backing up there's no risk to the wii by powering it off, the backup file just won't be complete. Restoring a backup is a different story.

Okay, thank you!