The news is blasting across Twitter right now:

Looks like both the northbound and the southbound lanes are out. The best person to follow for up-to-the-minute updates on Twitter at the moment is is Lynsi Burton, a reporter for the Skagit Valley Herald. KOMO radio is taking calls from witnesses. You can listen in on their website. One witness says a 50-foot portion of the bridge is gone and rescuers are on the scene. More updates as they come.

UPDATE 7:32 PM: Here's a picture from the scene:

UPDATE 7:34 PM: Based on witness reports and the above photo, it sounds like they're talking about this bridge, which was built in 1955 and which says got a satisfactory rating back in 2010:

Inspection (as of 08/2010)
Deck condition rating: Satisfactory (6 out of 9)
Superstructure condition rating: Fair (5 out of 9)
Substructure condition rating: Satisfactory (6 out of 9)
Appraisal: Functionally obsolete
Sufficiency rating: 57.4 (out of 100)

Average daily traffic (as of 2010)

UPDATE 7:40 PM: KING 5 has another photograph of the scene. At least two cars are in the water, and all north-south traffic is stopped.

UPDATE 7:48 PM: Holy shit, these pictures are incredible:

UPDATE 7:58 PM: I'm depositing more on-the-scene tweets after the jump, so this post will load in a timely fashion.

UPDATE 8:01 PM: KING 5 is streaming live from the scene right now.

UPDATE 8:22 PM: Marcus Deyerin on Twitter is saying that two people are being extracted from a truck that's in the water at the moment. Authorities are asking people to stop coming to the scene, as they're getting in the way. Also, they're asking residents of Skagit to stay off the phone if they can, as lines are getting tied up.

UPDATE 8:28 PM: Rescuers in boats are at the scene. I've put another photo after the jump.

UPDATE 8:30 PM: On Twitter, Skagit Valley Herald reporter Gina Cole says: "Stretcher with second person pulled from river. Unsure if person is alive, but no applause from onlookers this time when they reached land." KOMO says one person has been pulled from a car and two have been rescued from a truck. Here's a KOMO live feed.

UPDATE 8:35 PM: I've heard from multiple eyewitnesses on different news livestreams that the collapse appeared to happen because a wide load truck struck a beam on the bridge. We're a long way from discovering the reason for all this, though.

UPDATE 8:58 PM: The Seattle P.I. says the bridge was declared "safe and sound" by Washington's Department of Transportation in 2008.

UPDATE 9:05 PM: Brian Rosenthal at the Seattle Times writes:

Rescuers think they have pulled everybody out of the water, but they’re not sure, [Marcus] Deyerin [of the Northwest Washington Incident Management Team] said.

Anybody still in the water will probably not be rescued, officials said.

UPDATE 9:08 PM: And then there's this update, from the Everett Herald:

Governor Inslee and Transportation Secretary Lynn Peterson are about to get in a plane and fly to the scene.

UPDATE 9:17 PM: And with the news that there were no fatalities, that's the end of this live-Slog. Any new developments will appear as new posts on Slog tonight.