Just in from WSDOT: “A roll-over collision is blocking the three left lanes of southbound I-5, just south of Spokane Street in Seattle. Fire and aid are on scene. WSDOT Incident Response is en-route.” Here’s the camera (what it shows, depends on where its operators focus it):

11:05 AM UPDATE: WSDOT says the crash has cleared but traffic is backed up a few miles into downtown.