Site in 'Maintenance' mode- unable to remove


I have just used the ‘update all’ to update all of the wpmu plugins.

The site now says it is “Briefly unavailable for scheduled maintenance. Check back in a minute.”

I have not put it into maintenance mode, but assume the update of the plug-ins did this.

I cannot log in, as I just get the maintance mode issue. This is not an issue with the hosting, as other sites on the same host and server are working properly ( for example).

How can I remove the blog from maintenance mode so I can log-in, and so visitors can visit the website?