We first noticed it internally, and then saw reports on Twitter.
@SlackHQ also confirmed the service issue in a tweet:
The Slack System Status page has yet to catch up.
Just know you’re not alone.
We reached out to Slack and will continue to update as we know more.
Update 4:11pm ET: Slack has tweeted that it’s resolving things.
Further Update: Slack is back! Return to business as usual. /giphy breaktimeover