So I was stuck with two sentences instead of my blog: “Briefly unavailable for scheduled maintenance. Check back in a minute.” For a visitor this can be small inconvenience but for a blogger that’s a problem.
How to get out of this mess?
First you need FTP access to your hosting. When you log in, you will see a file called .maintenance.
After deletion just reload your blog and do whatever you need to do. And don’t forget to finish those updates ;).